[i]Proposition:[/i] On a parabola, every tangent line intersects a given tangent at the same focal angle.
Or, given two parabola tangents and their point of intersection, the tangents together with the three segments joining the Focus with the three points form a pair of similar triangles with
-equal angles at the focus
-the angle at the tangent point of one triangle is equal to the angle at the point of intersection of the other.
And other things that are significantly less confusing than they sound.
Step-by-step proof with Construction Protocol.
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Used in Parabola from four tangents: [url]http://www.geogebratube.org/material/show/id/38334[/url],
problem #45 in Heinrich Dorrie's [i]100 Great Problems of Elementary Mathematics.[/i]
