# Construction of complex points on a parabola using tangents

- Topic:
- Parabola

Shows how to construct the complex points on a parabola in a particular iplane using tangents. Drag the slider marked t to see the construction progress in the following steps:

- Draw a vertical line from P to the parabola and mark the point on the parabola. Let's call it A.
- Draw the tangent to the parabola at the point A.
- Copy the distance from A to P inside the parabola from A. Let's call this new point B.
- Draw a line through B parallel to the tangent at A and mark where it meets the parabola. Let's call these points C and D.
- Draw vertical lines through C and D.
- Draw a line through P parallel to the tangent at A. Mark where it meets the vertical lines through C and D.