Question

Find the angle between the given vectors to the nearest tenth of a degree.

u = <2, -4>, v = <3, -8>

3.0°

6.0°

-7.0°

16.0°

Answer 1

So far this is what I've got...

<2,-4> x <3,-8> = 6+32= 38

2^2 = 4
-4^2= -16
4+-16= -12 sqrt 12

3^2 = 9
-8^2 = -64
9+(-64)= -55 sqrt55

And then I did cos-1 (38/sqrt12 sqrt55)
and then that gives me error so I don't know what I'm doing wrong...

Answer 2

But I got error so where did I mess up?

Answer 3

http://www.mathsisfun.com/algebra/vectors-dot-product.html