Find Angle Between Vectors A & B: 105.27

[w0lfed]

Homework Statement

Find the angle between the following vectors?
A = -2.00i^ + 6.00j^ and B = 2.00i^ - 3.00j^ (the ^ means 'i hat')

Homework Equations

Theta = tan^-1 = (opposite/adjacent)

The Attempt at a Solution

i said for the first part of the component that
theta(A) = tan^1 (6/2) = 71.57
and then did the same for the other component
theta(B) = tan^1 (2/3) = 33.70

and the angle between them should be the addition of those two? ie 105.27?
im confused...this doesn't look right

 

[jeffreydk]

Have you done dot or cross products yet? If you have the easiest way to compute the angle is through the association that

$$\mathbf{A}\cdot\mathbf{B}=|\mathbf{A}||\mathbf{B}|\cos{\theta}$$

or with cross products

$$|\mathbf{A}\times\mathbf{B}|=|\mathbf{A}||\mathbf{B}|\sin{\theta}$$

where $\theta$ is the angle in between them.

 

[w0lfed]

nope, I've never seen that before?