I'm pretty sure I'm making this question a lot harder than it is... The question is this - "Three point charges are fixed to the corners of a square, one to a corner, in such a way that the net electric field at the empty corner is zero. Do these charges all have the same sign or the same magnitude but perhaps different signs?" My answer is the charges would have the same sign and different magnitudes because when calculating net electric fields the sign of the charge is not taken into account...is this right? Any advice would be fabulous! Thank you!