Two force, wherever you point it, it stays straight. These forces are equal in magnitude and opposite in sense, and have the same line of action. if i have a member with two points on it and forces acting on those points, it will be on the same line of action as those points. They will have opposite sense and same magnitude. They will have some angle, which you will know. this cuts it down to a single force that you have to solve for, regardless of what type of member it is. Prove that the forces are equal and that the lines of action are along an angle theta. HINT: Use to do equations of equilibrium.