Question

Show that cos3x=4cos^3 x-3cos x​

Answer 1

cos2x=cox^2 x-1

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