Comparing Areas!!

Geometry Level 2

If the triangle shown is an equilateral triangle, compare the orange area A o A_o and the purple area A p A_p ?

A o = A p A_o = A_p 3 A o = A p 3A_o = A_p A o > A p A_o > A_p 2 A o = A p 2A_o = A_p A o < A p A_o < A_p

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1 solution

Chew-Seong Cheong
Nov 13, 2019

Since the concentric center O O of the two circles is also the centroid of the equilateral triangle, if the radius of the orange circle is r r , the radius of the big circle is 2 r 2r .

We note that the purple area A p A_p is one-third of the area of the big circle minus the area of the orange circle. Then A p = π ( 2 r ) 2 π r 2 3 = π r 2 A_p = \dfrac {\pi(2r)^2 - \pi r^2}3 = \pi r^2 . Therefore A o = A p \boxed{A_o=A_p} .

Thank you, nice solution.

Hana Wehbi - 1 year, 7 months ago

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