= cos^4x - sin^4x= (cos^2x + sin^2x)(cos^2x - sin^2x)= (1)(1 - sin^2x - sin^2x)= 1 - sin^2x - sin^2x= 1 - 2sin^2x
2sin^2x-cos^4x=1-sin^4x
2sin^2x-cos^4x=cos4x
2sin^2x=0
2x=pin n e Z
x=pi/2n e Z
= cos^4x - sin^4x
= (cos^2x + sin^2x)(cos^2x - sin^2x)
= (1)(1 - sin^2x - sin^2x)
= 1 - sin^2x - sin^2x
= 1 - 2sin^2x
2sin^2x-cos^4x=1-sin^4x
2sin^2x-cos^4x=cos4x
2sin^2x=0
2x=pin n e Z
x=pi/2n e Z