... tiing, se duge dd thi ham sd tren doan [-27t; 27r] Dd thi ham sd duoc bidu dien tren hinh Hinh 11 X X cos—, ndu cos— > 2 X b) Ta cd cos— X X -cos—, ne'u cos— < 2 Vi vay, tit dd thi ham sd y = ... G «• 2x = - ° - 60° + it360°, it G X = 5° + /:180°, it G Z ...