Which of the following is equal to $cos\;3x$?

A) $4\;cos^3x - 3\;cosx$

B) $4\;cos^3x + 3\;cosx$

C) $3\;cosx - 4\;cos^3x$

D) $3\;cos^3x - 4\;cosx$
related to an answer for: What is the value of $3\:sinA-4\;sin^3A$?

Answer: $4\;cos^3x - 3\;cosx$

selected Mar 12, 2013 by pady_1