Construction of Parabola via Tangent Method:

Given the point A and B and the distance CD from AB to the vertex. Extend the axis CD and set off DE the same to CD. EA and EB are tangents to the parabola at A and B, respectively. Divide EA and EB into the similar number of equal parts or five here and number the division points as displayed in diagram.

Figure

Connect the corresponding points 1 and 1′, 2 and 2′, 3 and 3′ and so forth. These lines, as tangents of the required parabola form its envelope. Sketch the tangent curve.