y=cos＾2x-2sinxcosx-sin＾2x
=cos2x-sin2x
=√2(sinπ/4cos2x-cosπ/4sin2x)
=√2(-2x+π/4)
所以：函数y=cos＾2x-2sinxcosx-sin＾2x的值域是[-√2,√2]