Đặt `t=4sinx+3cosx=5sin(x+alpha)`
`=>tin[-5;5]` và `t≠-1`
`=>t+6/(t+1)=6`$\\$`<=>`\(\left[ \begin{array}{l}t=0\\t=5\end{array} \right.\) $\\$`=>`\(\left[ \begin{array}{l}5sin(x+\alpha)=0\\5sin(x+\alpha)=5\end{array} \right.\) $\\$`<=>`\(\left[ \begin{array}{l}x=-\alpha+kπ\\x=\dfrac{π}{2}-\alpha+k2π\end{array} \right.\) `(kinZZ)`$\\$Với `alpha` thỏa mãn:$\\$`{(sin alpha=3/5),(cosalpha=4/5):}`