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PROJECT EULER · #0471

Triangle Inscribed in Ellipse

Statement only · UnsolvedOriginal problem ↗

The triangle ABC is inscribed in an ellipse with equation x2a2+y2b2=1, 0<2b<a, a and b integers.

Let r(a,b) be the radius of the incircle of ABC when the incircle has center (2b,0) and A has coordinates (a2,32b).

For example, r(3,1)=12, r(6,2)=1, r(12,3)=2.

0471-triangle-inscribed-in-ellipse-1.png

0471-triangle-inscribed-in-ellipse-2.png

Let G(n)=a=3nb=1a12r(a,b)

You are given G(10)=20.59722222, G(100)=19223.60980 (rounded to 10 significant digits).

Find G(1011).

Give your answer in scientific notation rounded to 10 significant digits. Use a lowercase e to separate mantissa and exponent.

For G(10) the answer would have been 2.059722222e1.

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