Physics, electrostatics PLEASE HELP?

Question

Four point charges are put at the corners of a square with a length, x. Charge Q1 is the only positive charge in the bottom left-hand corner. Derive the equation to find the resultant force on the positive charge (Q1)

Answer 1

Use Coulomb's law : F=Kq1q2/r^2 solve in vector form then solve for magnitude.