Show that cos3x=4cos^3 x-3cos x

cos2x=cox^2 x-1

Step-by-step explanation:

1. If cosx=0 then equality is established

2. If cosx doesn't equal 0 then:

cos (2x+x) = 4cos^3 x-3cos x

cos2x*cosx-sin2x*sinx=4cos^2 x-3cosx

cos2x-2sin^2 x=4cos^2 x-3

cos2x=2+2cos^2 x-3

cos2x=cox^2 x-1

equality is established