Question

Verify the identity sin^2(x)cos^2(x)=1/8(1-cos(4x))

Answer 1

cos^2(x) = 1/2 + (1/2)cos(2x)

sin^2(x) = 1 - cos^2(x) = 1/2 - (1/2)cos(2x)

sin^2(x)cos^2(x)

= [1/2 - (1/2)cos(2x)][1/2 + (1/2)cos(2x)]

(a - b)(a + b) = a^2 - b^2

= (1/2)^2 - (1/2)^2[cos^2(2x)]

= 1/4 - (1/4)cos^2(2x)

= (1/4)[1 - cos^2(2x)]

= (1/4)[sin^2(2x)]

= (1/4)[1/2 - (1/2)cos(4x)]

= (1/4)(1/2)[1 - cos(4x)]

= (1/8)[1 - cos(4x)]