Coulomb's Law Question grade 12

jbjohnybaker

1. The problem statement, all variables and given/known data

Three point charges, q₁= -5.00 μC, q₂= -4.00 μC, and q₃ which is negative are arranged as shown on three corner of side a=0.500 m. The direction of the forces on q₁ is at +20.0° with respect to the + x axis. Calculate the magnitude of q₃. The diagram looks something like this:
---------(-) q2
| (square) |
| (square) |
| (square) |
(+)------(-) q3
q1



2. Relevant equations

F = kq1q2
------
r^2
3. The attempt at a solution
I used the above formula and I put q3 as a variable. I found the two forces, the first one which is what q1 exerts on q3 and the second which is what q2 exerts on q3:

F(1 on 3) = 1.69 X 10^5 x (q3)
F (2 on 3) = 1.44 x 10^5 x (q3)

But then I'm stuck...

jbjohnybaker

Anyone????