Vector Difference question??

Question

Find the direction of the vector difference A - B.

Ax=0

Bx=7.5

Ay= -8

By = 12.99

I have A - B = (Ax-Bx) + (Ay-By)

(0-7.5) + ( -8 -12.99)

-7.5i - 20.99j

tan(theta) = (-20.99/-7.5) = 70.3 degrees

But it says that's wrong!! what am I doing wrong? Please help!

Answer 1

Rx = 0 - 7.5 = -7.5

Ry = -8 - 12.99 = -20.99

Angle = arctan 21/7.5 = 70.3 degrees

From a sketch, the R vector is in Q3, so the angle is

180 + 70.3 = 250.3

You always have to make a sketch, at least I do.

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