If the lines aX^2 + 2hXY + bY^2 =0 form two sides

If the lines aX^2 + 2hXY + bY^2 =0 form two sides of a parrelologram amd the line lX + mY =1 is one diagonal,prove that the equation of other diagonal is , Y(bl – lm) = X(am – hl )