Similar Pentagon Areas Part 1

Geometry Level 3

Let a pentahat be a pentagon with the following properties:

  • Two adjacent right angles.
  • All sides congruent.

If the area of a pentahat is ( a + b c ) s 2 \left(a+\dfrac{\sqrt{b}}{c} \right)s^2 , where s s is the length of one of the sides, and a a , b b , and c c are positive integers with b b square-free, find a + b + c a+b+c .


The answer is 8.

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1 solution

Roger Erisman
Apr 7, 2016

Given a pentagon with two right angles and all congruent sides we have a square with an equilateral triangle on top.

The area of the square = s^2

The area of the triangle = sqrt(3)*s^2/4.

Total area = s^2 + sqrt(3)*s^2/4 = s^2 * (1 + sqrt(3) / 4)

a + b + c = 1 + 3 + 4 = 8

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