Consider the parabola y2=−4ax We want to replace the variables x and y by the parameter t. We see that the LHS is a square. ⇒ When x is parameterised, the RHS should become a perfect square. ⇒ The parameterised form of x should be −at2 y2=−4ax ⇒y2=−4a(−at2) ⇒y2=4a2t2 ⇒y=2at. ⇒ The parameterised form of y should be 2 at. Hence, the parametric coordinate of any point of the parabola y2=−4ax is (−at2,2at)