求函数y=lg(sin^2x-4cosx+19)的域值

问题描述:

求函数y=lg(sin^2x-4cosx+19)的域值

sin^2x-4cosx+19=1-cos^2x-4cosx+19=-cos^2x-4cosx-4+4+19=-(cosx^2+cosx+4)+23=-(cosx+2)^2+23 -9