00:01
Okay, so we have these two vectors u1 and u2.
00:03
So the first thing we want to do is check that this forms an orthogonal basis for r2.
00:08
So we just need to check that they're orthogonal.
00:11
So we need to check the dot product is equal to 0.
00:15
So u1 .u2, so the vector 41 .1 .1 .1, 12.
00:22
So this is going to be 4 times minus 3 plus 1 times 12, which is minus 12, plus 12, which is minus 12, which is 0, so they're orthogonal, and there's two of them.
00:34
So orthogonal implies linearly independent, and there are two of them, so they span r2.
00:40
So we've shown that this is an orthogonal basis.
00:43
The next thing we want to do is take the vector x to be 0 minus 51, and write this as a linear combination of u1 and u2.
00:56
So we want to write 0 minus 51 equals c times u1, plus c times u2 so we could do this in a few ways we could just solve the um the easiest way probably here is to solve the pair of simultaneous equations so c times u1 is 4 c1 c1 plus c2 u2 gives us minus 3 c2 12 c2 and then we have two equations we have 0 equals 4 c1 minus 3 c2 and we have minus 51 equals c1 plus 12 c2.
01:40
So then we have two equations we can solve for c1 and c2.
01:46
So this first equation, if we rearrange, gives us 3c2 equals 4c1.
01:52
Or in other words, we could write this as c1 is 3 over 4c2, for example...