Pratique du Shadowing: Independence, Basis, and Dimension - Apprendre l'anglais à l'oral avec YouTube
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So as long as I'm introducing the idea of a vector space,
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So as long as I'm introducing the idea of a vector space,
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I better introduce the things that go with it,
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the idea of its dimension,
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and all important, the idea of a basis for that space.
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That space could be all of three-dimensional space,
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the space we live in.
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In that case, the dimension is three.
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But what's the meaning of a basis,
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A basis for three-dimensional space.
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Or a basis for other spaces.
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OK, so I have to explain independence, basis, and dimension.
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Dimension's easy if you get the first two.
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OK, independence.
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Are those vectors independent?
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Well, if I draw them in three-dimensional space,
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I can imagine 215 going in some direction.
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Let me draw it.
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How's that?
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2, 1, 5, whatever.
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Grows there.
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That's A1.
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OK.
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Now, is A2 on the same line?
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If A2 is on the same line,
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then it would be dependent.
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The two vectors would be dependent if they're on the same line.
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But this one is not on that line.
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It's 4, 2, 0.
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So it doesn't go up at all.
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It's somewhere in this plane, 4, 2, 0.
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I'll say there.
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Whatever.
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A2.
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So those are independent.
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Now, where does, so their combinations give me a space.
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The combinations of A1 and A2 give me a plane,
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a flat plane, in three-dimensional space.
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That plane is, I would say, they span the plane.
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A1 and A2 span a plane.
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And here's the key word, span.
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So there are two vectors.
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They're in three-dimensional space.
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And the plane they span is all their combinations.
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That's what we're always doing,
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taking all the combinations of these vectors.
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OK.
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So actually, A1 and A2 are a basis for that plane.
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A1 and A2 are a basis for that plane because their combinations fill the plane.
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And also, they're independent.
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I need them both.
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If I throw away one,
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I would only have one vector left,
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and it would only span a line.
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OK, now let me bring in a third vector in three dimensions.
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Well, what shall I take for that third vector?
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Suppose I take a1 plus a2 as my third vector.
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So 6, 3, 5.
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What about the vector 6, 3, 5?
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Well, what do I know?
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It's obviously special.
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It's a1 plus a2.
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It's in the same plane.
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So if I took a3 equal 6,
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3, 5, that would be dependent.
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The three vectors would be dependent with that a3,
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they would span the plane still.
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Their combinations would still give the plane.
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But they wouldn't be a basis for the plane a1 and a2 and a3 together,
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that's too much.
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Too many vectors for a single plane.
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The vectors are dependent.
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And we don't, a basis has to be independent vectors.
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You have to need them all.
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We don't need all three here.
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So that's a dependent one.
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It can't go into a basis with a1 and a2,
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because the three vectors are dependent.
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Now let me make a different choice.
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So that was dead.
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That did not do it.
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All right, let me take a3 equal some other,
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not a combination of these,
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but headed off in some new direction.
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Well, I don't know what that new direction is.
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Maybe 1, 0, 0.
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What the heck?
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I believe, I hope I'm right,
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that 1, 0, 0 is not a combination here.
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I think 1, 0, 0 goes off.
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It's pretty short.
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There's a3.
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Better a3 than that loser 6, 3, 5.
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1, 0, 0 is a winner.
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These three vectors.
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So now a1, a2, and let me add in a3.
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all three of them span a.
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What do they span?
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What are all the combinations of a1, a2, a3?
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It's three-dimensional.
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It's the whole three-dimensional space.
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They span all of 3D, the whole three-dimensional space.
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They're a basis for the whole three-dimensional space.
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They're independent.
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So let me, do you see that picture before I move it?
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A1, A2, A3 are independent.
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None of them is a combination of the others.
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They fill a three-dimensional space.
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They're a basis for that three-dimensional space.
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And that space is the whole,
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in this example, is the whole of R3.
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So let me just write down on the next backward what I mean.
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Independent.
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Independent.
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So independent columns of a matrix,
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independent columns of a matrix A,
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means the only solution to A v equals 0 is v equals 0.
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So if I have independent columns,
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then I haven't got any null space.
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If I have independent columns,
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then the null space of the matrix is just the 0 vector,
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is the 0 vector.
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So let me write down that example again.
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A was the matrix 215, 420, 100.
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I believe that matrix has independent columns.
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So its column space is the full three-dimensional space.
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Its null space only contains,
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let me put it, make that clear that that's a vector.
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And now I'm ready to explain,
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write down the idea of a basis.
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So what is a basis for the space?
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A basis for a space, a subspace.
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Independent vectors, that's the key.
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independent vectors that span the space,
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the subspace, whatever it is.
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By the way, if the column space is all of three-dimensional space,
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as it is here, That's a subspace too.
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It's the whole space, but the whole space counts as a subspace of itself.
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And the 0 vector alone counts as the smallest possible.
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So if we're in three dimensions,
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the idea of subspaces has we have just the 0 vector, just one point.
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That's the smallest.
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We have the whole three-dimensional space.
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That's the biggest.
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And then we have all the lines through 0.
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Those are on the small side.
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We have all the planes through 0.
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Those are a bit bigger.
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So we have, and those dimensions are 0, 1, 2, 3.
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The possible dimensions is told to us by how many basis vectors we need.
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So let me look at that and then come to dimension.
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OK.
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So independent means that no other combination of the vectors,
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no combination of these vectors gives the 0 vector except to take 0 of that,
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0 of that, and 0 of that.
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Basis, so those are a basis for the column space because they're independent and their combinations give the whole column space.
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OK.
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And now I wanted to say something about dimensions.
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OK.
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Dimension.
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It's a number.
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It's the number of basis vectors.
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for the subspace.
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Oh, but you might say that the subspace has other bases,
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not just the one you happen to think of first.
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And I agree.
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Many different bases.
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All I need for this example,
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all I need to get a basis for,
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in this case, for three-dimensional space is I need three independent vectors, any three.
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But the point is, the point about dimension is that I need exactly three.
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I can never get two vectors that span all of R3.
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And I can never get four vectors that are independent in R3.
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If I have fewer than the dimension number, I don't have enough.
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They don't span.
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If I have too many than the dimension, they're dependent.
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They won't be independent.
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They can't be a basis.
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Every basis has the same number,
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and that number is the dimension of the subspace.
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All right.
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Let's just take an example, just with a picture.
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I'll stay in three-dimensional space,
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but my subspace will just be a plane.
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So here I'm in three-dimensional space.
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Good.
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Now I have my subspace is a plane.
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So it goes through the origin.
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But it's only a plane.
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So I'm expecting that I could take a vector in the plane.
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And I could take another vector in the plane.
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And they could be independent.
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They are.
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They're different directions.
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But I couldn't find a third independent vector in a plane.
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Every basis for the plane.
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So here, every basis for this plane
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contains two vectors, always two.
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And that number two is the dimension of a plane.
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Well, I'm just saying the plane there is two dimensional.
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It's not the same as R2.
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It's not the same.
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That plane is a plane in R3.
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It's not ordinary two-dimensional space.
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But its dimension is two,
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because it takes any vector.
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And if I didn't like the looks of this one,
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well, that's no problem.
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Let me go that way.
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That's just as good.
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Those two vectors are independent.
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They span the plane.
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They're a basis for the plane.
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The plane is two-dimensional.
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That's the set of key ideas.
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Independent, span, basis.
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Basis is fundamental.
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Basis is a bunch of vectors.
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And dimension is how many vectors.
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OK, those are key ideas in linear algebra.
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And you'll see them come into the big picture of linear algebra.
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Thank you.
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Thank you.
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Context & Background
The video titled "Independence, Basis, and Dimension" introduces fundamental concepts in vector space, which are integral to mathematics and physics. The speaker begins by discussing the importance of understanding the dimension of a space and the significance of a basis within that context. The explanation includes visual representations to illustrate complex ideas, making it easier for viewers, including English learners, to grasp these mathematical concepts through language. For those seeking to enhance their English speaking practice, engaging with this content not only aids in comprehension but also enriches vocabulary related to mathematics and science.
Top 5 Phrases for Daily Communication
- Independent vectors: Referring to vectors that are not on the same line, contributing to the diversity of a vector space.
- Span: This term indicates the way in which combinations of vectors can fill a certain space, which is essential in discussing dimensions.
- Basis: A set of vectors that, when combined, span a vector space; crucial for understanding relationships in geometry and algebra.
- Dimensional space: The measure of how many coordinates are needed to specify a point within that space, a vital concept in both mathematics and related discussions.
- Combinations of vectors: Refers to the various ways vectors can interact to form new dimensions or spaces, an important aspect for mathematical discussions.
Step-by-step Shadowing Guide
For English learners looking to improve their understanding and pronunciation through shadowing, the following steps will help when approaching the video:
- Watch the video once: Familiarize yourself with the general flow and context of the discussion. Pay attention to the speaker's tone and pacing, which can greatly aid in your IELTS speaking practice.
- Focus on phrases: As you watch the second time, jot down the top phrases mentioned above. Listen for how they are pronounced and used in context. This practice enhances both vocabulary and comprehension.
- Shadow the speaker: Play the video in short segments and repeat after the speaker. This will help you to improve your English pronunciation and fluency. Concentrate on mimicking the intonation and stress patterns.
- Pause and practice: After shadowing a segment, pause and try to recite the phrases or sentences from memory. This active recall will strengthen your grasp on the vocabulary.
- Engage in discussion: If possible, find a study partner to discuss the concepts of vector spaces, independence, and basis using the phrases you've learned. This will solidify your understanding and allow you to practice informal English conversation.
By following these steps, you can not only gain deeper knowledge about vector spaces but also enhance your shadow speak skills, making you more confident in your English communication.
Qu'est-ce que la technique du Shadowing ?
Le Shadowing est une technique d'apprentissage des langues fondée sur la science, développée à l'origine pour la formation des interprètes professionnels. Le principe est simple mais puissant : vous écoutez de l'anglais natif et le répétez immédiatement à voix haute — comme une ombre suivant le locuteur avec un décalage de 1 à 2 secondes. Les recherches montrent une amélioration significative de la précision de la prononciation, de l'intonation, du rythme, des liaisons, de la compréhension orale et de la fluidité.
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