e/

ĐKXĐ: ...

\(\Leftrightarrow\frac{2sin4x.cos2x}{cos2x}-2cos4x=2\sqrt{2}\)

\(\Leftrightarrow2sin4x-2cos4x=2\sqrt{2}\)

\(\Leftrightarrow sin4x-cos4x=\sqrt{2}\)

\(\Leftrightarrow\sqrt{2}sin\left(4x-\frac{\pi}{4}\right)=\sqrt{2}\)

\(\Leftrightarrow sin\left(4x-\frac{\pi}{4}\right)=1\)

\(\Leftrightarrow4x-\frac{\pi}{4}=\frac{\pi}{2}+k2\pi\)

\(\Rightarrow x=\frac{3\pi}{16}+\frac{k\pi}{2}\)

d/

Đặt \(sin2x-cos2x=\sqrt{2}sin\left(2x-\frac{\pi}{4}\right)=t\Rightarrow\left|t\right|\le\sqrt{2}\)

\(\Rightarrow t^2-3t-4=0\Rightarrow\left[{}\begin{matrix}t=-1\\t=4\left(l\right)\end{matrix}\right.\)

\(\Rightarrow\sqrt{2}sin\left(2x-\frac{\pi}{4}\right)=-1\)

\(\Leftrightarrow sin\left(2x-\frac{\pi}{4}\right)=-\frac{\sqrt{2}}{2}\)

\(\Leftrightarrow\left[{}\begin{matrix}2x-\frac{\pi}{4}=-\frac{\pi}{4}+k2\pi\\2x-\frac{\pi}{4}=\frac{5\pi}{4}+k2\pi\end{matrix}\right.\)

\(\Rightarrow\left[{}\begin{matrix}x=k\pi\\x=\frac{3\pi}{4}+k\pi\end{matrix}\right.\)

c/

\(\Leftrightarrow sin6x\left(cos3x-1-sin3x\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}sin6x=0\Rightarrow x=\frac{k\pi}{6}\\cos3x-sin3x=1\left(1\right)\end{matrix}\right.\)

\(\left(1\right)\Leftrightarrow sin3x-cos3x=-1\)

\(\Leftrightarrow\sqrt{2}sin\left(3x-\frac{\pi}{4}\right)=-1\)

\(\Leftrightarrow sin\left(3x-\frac{\pi}{4}\right)=-\frac{\sqrt{2}}{2}\)

\(\Rightarrow\left[{}\begin{matrix}3x-\frac{\pi}{4}=-\frac{\pi}{4}+k2\pi\\3x-\frac{\pi}{4}=\frac{5\pi}{4}+k2\pi\end{matrix}\right.\)

\(\Rightarrow\left[{}\begin{matrix}x=\frac{k2\pi}{3}\\x=\frac{\pi}{2}+\frac{k2\pi}{3}\end{matrix}\right.\)

sin3x + 1=2sin²2x

<=> sin3x + 1 = 2\(\dfrac{1-cos4x}{2}\)

<=> sin3x + 1 = 1 - cos4x

<=> sin3x = -cos4x

<=> sin3x + cos4x = 0

<=> \(\dfrac{\sqrt{2}}{2}\)sin3x + \(\dfrac{\sqrt{2}}{2}\)cos4x = 0 (chia 2 vế cho \(\sqrt{2}\)).

<=> cos\(\dfrac{\pi}{4}\)sin3x + sin\(\dfrac{\pi}{4}\)cos4x = 0

<=> sin (3x+\(\dfrac{\pi}{4}\)) = 0

<=> sin(3x+\(\dfrac{\pi}{4}\)) = sin0

<=> \(\left[{}\begin{matrix}3x+\dfrac{\pi}{4}=0+k2\pi\\3x+\dfrac{\pi}{4}=\pi-0+k2\pi\end{matrix}\right.\)(k\(\in\)Z)

<=>\(\left[{}\begin{matrix}x=-\dfrac{\pi}{12}+\dfrac{k2\pi}{3}\\x=\dfrac{5\pi}{12}+\dfrac{k2\pi}{3}\end{matrix}\right.\)(k\(\in\)Z)

1.

\(\Leftrightarrow cos3x+sin3x-2sin3x.cos3x=0\)

\(\Leftrightarrow cos3x+sin3x-\left(2sin3x.cos3x+1\right)+1=0\)

\(\Leftrightarrow cos3x+sin3x-\left(sin3x+cos3x\right)^2+1=0\)

\(\Leftrightarrow\left[{}\begin{matrix}sin3x+cos3x=\frac{\sqrt{5}+1}{2}\\sin3x+cos3x=\frac{1-\sqrt{5}}{2}\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}sin\left(3x+\frac{\pi}{4}\right)=\frac{\sqrt{10}+\sqrt{2}}{4}>1\left(l\right)\\sin\left(3x+\frac{\pi}{4}\right)=\frac{\sqrt{2}-\sqrt{10}}{4}\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}3x+\frac{\pi}{4}=arcsin\left(\frac{\sqrt{2}-\sqrt{10}}{4}\right)+k2\pi\\3x+\frac{\pi}{4}=\pi-arcsin\left(\frac{\sqrt{2}-\sqrt{10}}{4}\right)+k2\pi\end{matrix}\right.\)

\(\Leftrightarrow x=...\)

2.

\(\Leftrightarrow sinx-\left(1+cosx\right)+sin2x=-2\)

\(\Leftrightarrow sinx-cosx+1+sin2x=0\)

\(\Leftrightarrow sinx-cosx-\left(1-2sinx.cosx\right)+2=0\)

\(\Leftrightarrow sinx-cosx-\left(sinx-cosx\right)^2+2=0\)

\(\Leftrightarrow\left[{}\begin{matrix}sinx-cosx=-1\\sinx-cosx=2\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}sin\left(x-\frac{\pi}{4}\right)=-\frac{\sqrt{2}}{2}\\sin\left(x-\frac{\pi}{4}\right)=\sqrt{2}>1\left(l\right)\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x-\frac{\pi}{4}=-\frac{\pi}{4}+k2\pi\\x-\frac{\pi}{4}=\frac{5\pi}{4}+k2\pi\end{matrix}\right.\)

\(\Leftrightarrow x=...\)

d/

\(\Leftrightarrow sin2x=sin6x-sin4x\)

\(\Leftrightarrow2sinx.cosx=2cos5x.sinx\)

\(\Leftrightarrow sinx\left(cosx-cos5x\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}sinx=0\\cos5x=cosx\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x=k\pi\\5x=x+k2\pi\\5x=-x+k2\pi\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x=k\pi\\x=\frac{k\pi}{2}\\x=\frac{k\pi}{3}\end{matrix}\right.\) \(\Leftrightarrow\left[{}\begin{matrix}x=\frac{k\pi}{2}\\x=\frac{k\pi}{3}\end{matrix}\right.\)

a/ Bạn coi lại vế trái đề bài, nhìn không hợp lý

b/ \(\Leftrightarrow\frac{1}{2}sin9x-\frac{1}{2}sinx=\frac{1}{2}sin5x-\frac{1}{2}sinx\)

\(\Leftrightarrow sin9x=sin5x\)

\(\Leftrightarrow\left[{}\begin{matrix}9x=5x+k2\pi\\9x=\pi-5x+k2\pi\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x=\frac{k\pi}{2}\\x=\frac{\pi}{14}+\frac{k\pi}{7}\end{matrix}\right.\)

c/ \(\Leftrightarrow sin2x-cos2x=cosx-sinx\)

\(\Leftrightarrow\sqrt{2}sin\left(2x-\frac{\pi}{4}\right)=\sqrt{2}cos\left(x+\frac{\pi}{4}\right)\)

\(\Leftrightarrow cos\left(\frac{3\pi}{4}-2x\right)=cos\left(x+\frac{\pi}{4}\right)\)

\(\Leftrightarrow\left[{}\begin{matrix}\frac{3\pi}{4}-2x=x+\frac{\pi}{4}+k2\pi\\\frac{3\pi}{4}-2x=-x-\frac{\pi}{4}+k2\pi\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x=\frac{\pi}{6}+\frac{k2\pi}{3}\\x=\pi+k2\pi\end{matrix}\right.\)