We can use the following equation to determine the value of 165 degrees;
1 - cos(2x)
_______ = sin²x
2
Here x = 165 degrees, as we want to prove the value of sin(165)
So that would make 2x = 165(2) = 330. We know cos(330) = √3/2. If we substitute;
1 - √3/2
_______ = sin²x,
2
sin = √(1 - √3/2)/2 = √((2 - √3)/4) = √2(√3 - 1) / 4
= √3 - 1 / 2√2 (Proved)