Which of the following numbers most accurately area of a regular decagon with side s = 2 cm?

(A) 9.51 cm2
(B) 20 cm2
(C) 30.78 cm2
(D) 31.84 cm2
(E) 32.90 cm2


S =  30.7768
x = (Correct answer is: C) Wrong answer


n=10 a=2  α=2π2 n=2 3.14162 100.3142  tanα=a/2:h h=a/2/tan(α)=2/2/tan(0.3142)3.0777  S1=a h2=2 3.077723.0777  S=n S1=10 3.0777=30.7768

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