dung la can 3 pan a mjnh gian nhu ri pan xem co dung ko nha : tach-5=-2-3 :-3can2sinx=-2can2sinx-can2sinx;2can2cosx=can2cosx+can2cosx rôi nhom lai xuat hien 2 cung xet denta ta thay den ta <or=0 co nghiem<=>denta=0=>ta tim dk x neu mjnh giạ nhu ri thi co ngiem nhung may dua trong lop toan la vo ngiem kiem tra giup mjnh voi nha