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**In Figure 13-34, a square of edge length 22.0 cm is formed by four spheres of masses m1 = 7.00 g, m2 = 3.50 g, m3 = 1.50 g, and m4 = 7.00 g. In unit-vector notation, what is the net gravitational force from them on a central sphere with mass m5 = 2.30 g?**

Okay this is what I did so far.

Since m4 and m1 are equal, they can be neglected. This leaves....

F = Gm5(m2-m3) / r^2

I then tried to multiply it by cos 45 degrees to get the i component and sin 45 degrees to get the y component, but this isn't working. Why is that?