... sin 2x 3 cos2x=+, Điều kiện ab t ab−+=−≤≤=+ 22 22 22 Thì 13t 2 sin 2x cos 2x 2cos 2x 22 ⎛⎞6π⎛⎞=+=⎜⎟⎜⎟⎜⎟⎝⎠⎝⎠− Vậy (*) thành: −= ⇔ −− =⇔= ∨=− 22 t5t5 2tt100 t (loại)t 22 2 ... ()=≠±⎡⎢⇔−⎢=⎢+⎣⇔=∨+=−⇔=∨+=cos2x 0 nhận do 111sin 2x 1 cos2xcos2x 0 1 cos2x sin2xcos2x 0 sin 2x cos2x 1− 1cos2x 0 sin 2x sin44 2 52x k 2x k2 2x k2 ,k 24 4 44ππ⎛⎞ ⎛⎞⇔=∨ +=−=−⎜⎟ ⎜⎟⎝⎠ ... k,k 42 122 π⇔=π+π =−+π∈ππ π π⇔=+ =− + ∈¢¢ Cách khác : ()(*) 2 2 1 sin 2x 3 sin 4x 0⇔− + = 2 2 cos 2x 2 3 sin 2x cos2x 0cos2x0cos2x 3sin2x0cos2x 0 cot g2x 3⇔+ =⇔=∨+⇔=∨ =−= 2x...