`y=sin^2 5x+cos^2 5x+3sin 2x-2` `TXĐ: R`
`y=1+3sin 2x-2`
`y=3sin 2x-1`
Ta có: `-1 <= sin 2x <= 1`
`<=>-3 <= 3sin 2x <= 3`
`<=>-4 <= y <= 2`
`=> y_[mi n]=4<=>sin 2x =-1<=>x=-\pi/4 + k\pi` `(k in ZZ)`
`y_[max] = 2<=>sin 2x=1<=>x=\pi/4+k\pi` `(k in ZZ)`