buktikan identitas trigonometri di bawah ini: cos 3t= 4 cos³ t- 3 cos t (gunakan kesamaan sudut ganda)

[tex]\cos(3t)=\cos(2t+t)=\cos(2t)\cos(t)-\sin(2t)\sin(t) \\ (2\cos^2(t)-1)\cos(t)-2\sin(t)\cos(t).\sin(t) \\ 2\cos^3(t)-\cos(t)-2\sin^2(t)\cos(t) \\ 2\cos^3(t)-\cos(t)(2\sin^2(t)+1) \\ 2\cos^3(t)-\cos(t)(2(1-\cos^2(t))+1) \\ 2\cos^3(t)-\cos(t)(2-2\cos^2(t))+1) \\ 2\cos^3(t)-\cos(t)(3-2\cos^2(t)) \\ 2\cos^3(t)+2\cos^3(t)-3\cos(t) \\ 4\cos^3(t)-3\cos(t)[/tex]