y=3-4sinx-4(1-sin^2x)
=4sin^2x-4sinx-1
=4(sinx-1/2)^2-2
当sinx=1/2时 ymin=-2
当sinx=-1时 ymax=7请问3-4sinx-4(1-sin^2x)到4sin^2x-4sinx-1是怎么变的谢谢配方=4(sin^2x-sinx)-1=4(sin^2x-sinx+1/4-1/4)-1=4(sin^2x-sinx+1/4)-2=4(sinx-1/2)^2-2cosx怎么不见了4cosx^2=4(1-sin^2x)