Vector Addition Question: find angle (A+B & A-B)

[alexi_b]

Homework Statement

Two vectors A and B have precisely equal magnitudes. For the magnitude of A + B to be 65 times greater than the magnitude of A - B, what must be the angle between them?

Homework Equations

The Attempt at a Solution

I tried using the dot product and solving for the angle but i don't know if my math was right. I keep getting a relatively small angle which I know is around the right answer but its still off somehow. Please help!

 

[magoo]

Try something like A = a + jb, where a and b are the components of A.

 

[alexi_b]

Try something like A = a + jb, where a and b are the components of A.

can you elborate? I am not quite sure what you mean

 

[haruspex]

I tried using the dot product and solving for the angle but i don't know if my math was right. I keep getting a relatively small angle which I know is around the right answer but its still off somehow.

Please post your working. We can rarely tell where you are going wrong from a rough outline.