sin^4x-5sin4x=6 giải giúp mình với ạ!!

\[\begin{array}{l} {\sin ^4}x - 5\sin 4x = 6\\ \Leftrightarrow {\sin ^4}x = 6 + 5\sin 4x\\ Ta\,\,co:\,\,0 \le {\sin ^4}x \le 1\\ \Rightarrow 0 \le VT \le 1\\ - 1 \le \sin 4x \le 1 \Rightarrow - 5 \le 5\sin 4x \le 5\\ \Leftrightarrow 1 \le 5\sin 4x + 6 \le 11\\ \Rightarrow 1 \le VP \le 11\\ \Rightarrow pt\,\,co\,\,nghiem\,\, \Leftrightarrow \left\{ \begin{array}{l} {\sin ^4}x = 1\\ 6 + 5\sin 4x = 1 \end{array} \right.\\ \Leftrightarrow \left\{ \begin{array}{l} \left[ \begin{array}{l} \sin x = 1\\ \sin x = - 1 \end{array} \right.\\ \sin 4x = - 1 \end{array} \right.. \end{array}\]