Each corner of a right angled triangle is occupied by identical point charges "A", "B", and "C" respectively. Draw a sketch of this arrangement. "A" exerts force F on "B". An equal force F is exerted by "C" on "B" (/_ ABC= 90 degrees). Determine an expression for the net force on "B".

Hello!
Because the charges are identical, they repel each other. Therefore the direction of the force that A exerts on B is directed from A to B (outside the triangle ABC ). The direction of the force that C exerts on B is from C to B (also outside the triangle ABC ).
The net force is the vector sum of these two forces. Both forces have equal magnitude F and the angle between them is 90 degrees, and the magnitude of the net force is the length of the hypotenuse of a right triangle with the legs of length F. It is F*sqrt(2) (this is the answer for "an expression").
The direction of the net force is 45 degrees to both forces outside of the triangle ABC, because the parallelogram of forces is a square in this case. Please look at the picture attached.