Can you help me with this Calculus problem?

Question

I need to find the vector projection of vector B onto vector A. Vector A = (-3,4) Vector B = (3,0).

I got my answer to be ( (27/25), (-36/25) ). The latter coordinate is correct, but I believe the former coordinate is inaccurate. Any help on what I am doing wrong would be greatly appreciated.

Answer 1

The projection of B on A is:

[ (A . B) A ] / | A |^2

= (- 3 * 3 + 4 * 0)(- 3, 4) / (3^2 + 4^2)

= -9(- 3, 4) / 25

= (27 / 25, - 36 / 25).