perplexus.info :: Just Math : Golden sine

Golden sine (Posted on 2023-09-17)

Prove that sin³18 + sin²18 = 1/8.

No Solution Yet Submitted by Danish Ahmed Khan

Rating: 4.0000 (1 votes)

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re: proof found

| Comment 2 of 3 |

(In reply to proof found by Steven Lord)

Sin 18 degrees = (v5-1)/4

=> sin^2(18) = (3-v5)/8

Now, sin^3(18)+ sin^2(18)

=sin^2(18)(sin(18)+1)

= (3-v5)/8* (v5+3)/4

= (9-5)/32

=4/32

=1/8

Edited on September 17, 2023, 11:00 pm

Posted by K Sengupta on 2023-09-17 23:00:04

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