Area Problem #19

area19

A regular pentagon ABCDE is inscribed in a circle as shown.

Write a formula for the area of the smaller circle inscribed in BCD in terms of r1, the radius of the larger circle.

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4 thoughts on “Area Problem #19

  1. It’s late and I should check but I think it is
    area = pi * (0.309017*r1) ^ 2

    0.309.. = (cos (18) * sin(3*18) (1- sin (18)))/(sin (4* 18)+cos(18)sin(3*18))

    Used sine rule and a congruent triangle and a few other obv things

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