\(cos^4\dfrac{x}{2}+sin^4\dfrac{x}{2}+2sinx=1\)
\(\Leftrightarrow\left(cos^2\dfrac{x}{2}+sin^2\dfrac{x}{2}\right)^2-2sin^2\dfrac{x}{2}.cos^2\dfrac{x}{2}+2sinx=1\)
\(\Leftrightarrow1-\dfrac{1}{2}sin^2x+2sinx=1\)
\(\Leftrightarrow sinx\left(4-sinx\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}sinx=0\\sinx=4\left(vn\right)\end{matrix}\right.\)
\(\Rightarrow x=k\pi\)
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