If a tangent to the parabola y2=4ax meets the x-axis at T and the tangent at the vertex A, at P. Let the rectangle TAPQ be completed. Then the locus of the point Q is
a parabola
The tangent at any point B(at2,2at) to the parabola is ty=x+at2 .......(1)
Since tangent at the vertex A is the y-axis, T and P are (−at2,0) and (0,at) respectively. Clearly A is (0, 0)
If Q be(h, k), then h =AT =−at2 and k= AP = at Eliminating t, we get k2+ah=0
Hence the locus of Q is y2+ax=0, which is parabola.