Point charges q=4.0X10^-9 C are placed at each of three corners of a square, the sides of which are L=15cm. Discover both the magnitude and the direction of the electric field at the vacant corner of the square (which is placed in vacuum). Use algebraic symbols in your derivation, and only put in numbers, with units, when you have obtained a final expression for the electric field. Be sure to treat important figures correctly.