If is the area of an ellipse with an eccentricity of and is the area of the shape bounded by the set of points for which two tangents of that ellipse meet at a right angle, then , where and are positive co-prime integers. Find .
This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try
refreshing the page, (b) enabling javascript if it is disabled on your browser and,
finally, (c)
loading the
non-javascript version of this page
. We're sorry about the hassle.
Since e = 2 5 7 = a c , c = 7 k and a = 2 5 k , and since a 2 − b 2 = c 2 in an ellipse, b = 2 4 k .
The area of an ellipse is A = π a b , so A E = 6 0 0 π k 2 .
The set of points for which two tangents of any curve meet at a right angle is an orthoptic , and an orthoptic for any ellipse is a circle with a radius of a 2 + b 2 , and therefore an area of A = π ( a 2 + b 2 ) , so A F = 1 2 0 1 π k 2 .
Therefore, A F A E = 1 2 0 1 π k 2 6 0 0 π k 2 = 1 2 0 1 6 0 0 , so p = 6 0 0 , q = 1 2 0 1 , and p + q = 1 8 0 1 .