00:01
We want to find the angle between the vectors u is equal to 2 i plus j and v is equal to i plus 2 j minus k to the nearest hundredth of a radium so on the board i have the two definitions of dot product and if we rewrite the first definition here we can solve for cosine so that gives us cosine of theta is equal to, so u.
00:39
.v over the magnitude of you times the magnitude of v.
00:47
And if we were to take the inverse of cosine on each side, that would tell us that theta is equal to cosine inverse of u.
01:00
.
01:00
Over the magnitude of you times the magnitude of v.
01:08
So if we go ahead and find the dot product of these two vectors and their magnitudes, we can solve for theta.
01:17
So let's go ahead and do that.
01:19
Now, the second definition of dot product i have here written in green.
01:25
And so remember the u1, u2, u3, and as well as for the vs.
01:30
So the ones with the one subscript are our x term, the two is our y, and the three is are z.
01:41
And we can go ahead and correspond these to get...
01:45
So, u1, well, the x term goes with the i component, so that's going to be 2.
01:54
U2 goes with the j component because that's our y component, so u2 is going to be 1...