P = X2-X1 R = Y2-Y1 PP = P^2 PPP = P*PP Q = X1*PP t0 = R^2 t1 = 2*Q t2 = t0-PPP X3 = t2-t1 t3 = Q-X3 t4 = Y1*PPP t5 = R*t3 Y3 = t5-t4 ZZ3 = PP ZZZ3 = PPP