Question

函数y=sinx的4次方+cosx的4次方的值域是

Answer 1

y=[(sinx)^2+(cosx)^2]^2-2(sinx)^2+(cosx)^2

=1^2-1/2*(2sinxcosx)^2

=-1/2*(sin2x)^2+1

=-1/2*(1-cos4x)/2+1

=1/2*cos4x+1/2

-1