1,Pt\(\Leftrightarrow2sin^22x+2.sin2x.cos2x+2\left(sin^22x+cos^22x\right)=0\)
\(\Leftrightarrow2sin^22x+sin2x.cos2x+cos^22x=0\) (vô nghiệm)
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2, Pt \(\Leftrightarrow-\left(sinx+3\right)sin^2\dfrac{x}{2}\left(1-sin^2\dfrac{x}{2}\right)+1=0\)
\(\Leftrightarrow-\left(sinx+3\right)sin^2\dfrac{x}{2}.cos^2\dfrac{x}{2}+1=0\)
\(\Leftrightarrow-\dfrac{\left(sinx+3\right).sin^2x}{4}+1=0\)
\(\Leftrightarrow-sin^3x-3sin^2x+4=0\)
\(\Leftrightarrow\left(sinx-1\right)\left(sinx+2\right)^2=0\)
\(\Leftrightarrow\left[{}\begin{matrix}sinx=1\\sinx=-2\left(ktm\right)\end{matrix}\right.\)\(\Rightarrow x=\dfrac{\pi}{2}+k2\pi\left(k\in Z\right)\)
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