1. The problem statement, all variables and given/known data 3 point charges L(-b, b) M(b, b) & N(0, 0) have charges Q, -3Q & Q. I need to find the force on the charge at the origin. 2. Relevant equations Coulomb's Law important, here. F = 1/4∏0 q^2/r^2 r(hat) z-component no existent (from coordinates given) x- & y-components to be found Now, I'm finding it difficult to see thew wood from the trees with this relatively simple thing. I'm trying to find the x- & y- bits of force between the charges 1 & 2 to the charge at the origin for each charge. 3. The attempt at a solution Now, F = 1/4∏ε0 ((Q(2b*-cos45)*Q)/(2cos45)) - (-3Q(2b*cos45)/(2cos45) Then factor out the Q^2/r^2 terms. I would like it in the form F=1/4∏ε0 (Q^2/r^2) (!!ex - !!ey) but am finding the (!!ex - !!ey) bit difficult to get due to the trig bits I think. Advice needed, please. I'm sure this is wrong, but is the main stumbling block. If I can get this then magnitude of force & direction of unit vector will be easy.