I have worked out how to do it, just I need to know how to solve it without calculator.
Find the exact value of:
2 cos²15 - 1
this is what i did:
2 cos²15 - 1 so
= cos²15 + sin²15 = 1 side note: sin²15 = 1 - cos²15 hence: 2 cos²15 - 1
then i did:
2 cos²15 - 1 would initially be: cos²15 + sin²15
= cos(15 + 15)
= cos 15 x cos 15 - sin 15 x sin 15
= root 3 / 2
What i wanna know is, i could not of done this without a calculator...
What is the alternative method?
(sorry if i made this very confusing)