分からない問題はここに書いてね464

>>904
L = 1 + 1 + 2cos(36) = 2{1 - cos(144)} = 4sin(72)^2 = 2 + φ = φ√5 = 3.618034
S = (1/2)sin(72) = 0.475528258
S/(L^2) = 1/{32sin(72)^3} = (1/20)√(5-2√5) = 0.036327126
でいい。
(舐籤形は (1/20)sin(72) = 0.047552826　で大きい。)

cos(36) = φ/2 = 0.809017
sin(72) = √{(5+√5)/8} = (1/2)√(2+φ) = (1/2)√(φ√5) = 0.951056516