Question

Can anyone can prove this..

Answer 1

\[\cos 3\theta= 4\sin ^{3}\theta -3\cos \theta \]

Answer 2

@iGreen

Answer 3

@perl

Answer 4

let t = theta
cos(2t + t ) = cos(2t)cost - sin(t)sin(2t)

Answer 5

that formula is incorrect, above

Answer 6

plug in theta = 0

cos (3*0) != 4 sin(0)^3 - 3 cos(0)

1 != 4*0 - 3*1

Answer 7

ok

Answer 8

so you're done :) you have a counterexample, and it is a false statement generally

Answer 9

oh! is that it :D ?

Answer 10

you cant prove a false statement
unless theres a typo