What is the range of f(x)=sin4x+cos4xf(x) = \sin^4 x + \cos^4 xf(x)=sin4x+cos4x?
[0.5,1][0.5, 1][0.5,1]
[0,1][0, 1][0,1]
[1,2][1, 2][1,2]
[0.75,1][0.75, 1][0.75,1]