describe 2 ways you can find the angle between 2 vectors.?

Question

i have one... to use the formula:

cos(theta)=a.b/|a| |b|


whats the other way?

Answer 1

One way is to use the dot product.

a • b = || a || || b || cosθ
cosθ = (a • b) / (|| a || || b ||)

The other way is to use the magnitude of the cross product.

|| a X b || = || a || || b || sinθ
sinθ = || a X b || / (|| a || || b ||)

Please note, you need to use the MAGNITUDE of the cross product.

Answer 2

If my memory serves me right, u can use

Tan(theta) = |b|/|a|