Question

Prove that sin squared 20 degrees+sin squared 40 degrees+ sin squared 80 degrees is equal to 3/2

Answer 1

sin^2(20) = 0.116,997,778.
sin^2(40) = 0.413,175,911.
sin^2(80) = 0.969,846,310.

Sum = 1.500 = 1 1/2 = 3/2.