How to find a tangent line of ellipse

Let A be a point in the ellipse.

step 1:

Let A be a vertex, then draw a pentagram which inscribed in the ellipse.

 

step 2:

Let F be the intersection point of the straight line through A,D and the straight line through C,E.

Let G be the intersection point of the straight line through A,C and the straight line through B,D.

Draw a straight line through F and G.

step 3:

Let H be the intersection point of the straight line through F,G and the straight line through B,E.

Draw a straight line through A and H.

Then the straight line through A and H will be the tangent line of ellipse at point A.

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Pascal's Thm