bạn gõ latex cho chuẩn hoặc vt ra giấy đc k ạ?
\(\Leftrightarrow\left(1-\cos2x\right)\cdot\dfrac{1}{2}+4\cdot\dfrac{1}{2}\cdot\left(\cos2x+1\right)-2\sin2x=0\)
\(\Leftrightarrow\dfrac{1}{2}-\dfrac{1}{2}\cos2x+2\cos2x+2-2\sin2x=0\)
\(\Leftrightarrow-2\sin2x+\dfrac{3}{2}\cos2x=-\dfrac{5}{2}\)
\(\sqrt{\left(-2\right)^2+\dfrac{9}{4}}=\dfrac{5}{2}\)
Chia hai vế cho 5/2, ta được:
\(-\dfrac{4}{5}\sin2x+\dfrac{3}{5}\cos2x=-1\)
\(\Leftrightarrow\sin a\cdot\cos2x-\sin2x\cdot\cos a=-1\) với sina=3/5; cosa=4/5
\(\Leftrightarrow\sin\left(a-2x\right)=-1\)
\(\Leftrightarrow a-2x=-\dfrac{\Pi}{2}+k2\Pi\)
\(\Leftrightarrow2x=a+\dfrac{\Pi}{2}-k2\Pi\)
hay \(x=\dfrac{a}{2}+\dfrac{\Pi}{4}-k\Pi\)
\(\Leftrightarrow sin^2x-4sinxcosx+\left(2cosx\right)^2=0\)
\(\Leftrightarrow\)\(\left(sinx-2cosx\right)^2=0\)
\(\Leftrightarrow sinx=2cosx\)
\(\Rightarrow......\)
