PreCalculus Questions

Question

Given u = -10i + 6j and v = -8i + -j, find the angle between u and v.

Answer 1

θ = cos^-1[u·v / (|u||v|)]

 

u·v = (-10)(-8) + (6)(-1) = ?

 

|u| = √[(-10)² + (6)²] = ?

|v| = √[(-8)² + (-1)²] = ?

 

Plug in the numbers and evaluate.  Recall that cos^-1(x) is multivauled.  The correct angle will be the smaller of the two.