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What is the diagonal of a regular pentagon whose radius is 20 cm?

 Apr 29, 2024
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Diagonal^2  =  20'2 + 20^2 -2 ( 20 *20) * cos (144°)

 

Diagonal^2  =  800 - 800 *(-1 - sqrt 5) / 4

 

Diagonal  =   sqrt [ 800 + 200 ( 1 + sqrt 5) ] =  10 sqrt [ 10 + 2sqrt 5 ] = 10 [ 2 (5 + sqrt 5)] ≈ 38.04

 

cool cool cool

 Apr 30, 2024

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