Prove that if P(a,b) is a point on the rotated
ellipse C (whose equation is ), then so is Q(-a,-b), and that the tangent lines to C at P and Q are parallel. The equation of the line joining P and Q is y - b = m(x - a), where , then the equation of the line is . Now, do I substitute for y into the equation for C? To prove the tangent lines are ...