f(3x) = 4(f(x))^3 - 3f(x)" alt="f(x) = cos(3x) = cos(2x+x) = cos2x*cosx - sin2x*sinx = (2cos^2x-1)cosx-2sin^2xcosx = 2cos^2x-cosx-2cosx(1-cos^2x) = 2cos^3x-cosx-2cosx+2cos^2x = 4cos^3x-3cosx => f(3x) = 4(f(x))^3 - 3f(x)" align="absmiddle" class="latex-formula">