00:01
So we know if we have a pair of vectors, u and v, then the angle between those vectors is going to be given as theta, which is going to be the inverse cosine of we take u dotted with v divided by the magnitude of u times the magnitude of v.
00:16
So first we find the magnitude of u.
00:21
So we find that the magnitude of u, we take the square root of, well, take the dot product of u with itself.
00:28
So it's a square root of 1 times 1 minus 1 times negative 1 plus 2 times 2.
00:34
And then we have a negative 2 times negative 2.
00:36
So that's the square root of 1 plus 1 plus 4 plus 4.
00:39
So that's going to be the square root of 10.
00:45
And so that's the magnitude of u.
00:47
And then we find the magnitude of v in the same way.
00:51
So the magnitude of v is the square root of the dot product of v with itself.
00:57
So that's the square root of the 2 times 2 plus 2.
01:00
3 times 3 plus 4 times 4 plus 5 times 5, giving us the square root of 4 plus 9 plus 16 plus 25.
01:07
So this is a square root of 54, which is equal to, well, 3 times the square root of 6.
01:15
54 is 9 times 6, right? and square root of 9 is 3...