= (4cos^4 x) + (sin^4 x)= (4cos^4 x) + (1 - cos^2 x)^2= (4cos^4 x) + (1 - 2cos^2 x + cos^4 x)= 1 + 2cos^4 x
= (4cos^4 x) + (sin^4 x)
= (4cos^4 x) + (1 - cos^2 x)^2
= (4cos^4 x) + (1 - 2cos^2 x + cos^4 x)
= 1 + 2cos^4 x