How would I solve E1jk without the summation? I know how to solve it using the summation symbol but don't know howto do it without it. Also, I need help proving that |torque|^2 = |r x F|^2= r^2F^2sin@(thetarF ). r dot F = rF cos (thetarF . Would I have to use (r x F) dot (r x F)?