\(\Leftrightarrow\frac{cos2x.cos4x.cos8x}{cos^2x.cos^22x.cos^24x}=8\)
\(\Leftrightarrow\frac{cos8x}{cos^2x.cos2x.cos4x}=8\)
\(\Leftrightarrow cos8x=8cos^2x.cos2x.cos4x\)
Do \(sinx=0\) ko phải nghiệm
\(\Leftrightarrow sinx.cos8x=cosx.8sinx.cosx.cos2x.cos4x\)
\(\Leftrightarrow sinx.cos8x=cosx.sin8x\)
\(\Leftrightarrow sin\left(8x-x\right)=0\Leftrightarrow sin7x=0\)
giải pt
a) \(tanx.tan\frac{\pi}{9}=1+tan\frac{\pi}{9}.tan\frac{\pi}{90}+tanx.tan\frac{\pi}{90};\left(-2\pi< x< 2\pi\right)\)
b) \(tan^22x+\frac{1}{cos^22x}=7;\left(0< x< 360^0\right)\)
c) \(tan^3x+\frac{1}{cos^2x}+4\sqrt{3}\left(1+tanx\right)=8+7tanx;\left(-\pi< x< \pi\right)\)
giải pt : 1, \(\dfrac{\left(1-cosx\right)^2+\left(1+sinx\right)^2}{4\left(1-sinx\right)}-tan^2sinx=\dfrac{1}{2}\left(1+sinx\right)+tan^2x\)
Giải các phương trình :
a) \(\tan\left(2x+45^0\right)=-1\)
b) \(\cot\left(x+\dfrac{\pi}{3}\right)=\sqrt{3}\)
c) \(\tan\left(\dfrac{x}{2}-\dfrac{\pi}{4}\right)=\tan\dfrac{\pi}{8}\)
d) \(\cot\left(\dfrac{x}{3}+20^0\right)=-\dfrac{\sqrt{3}}{3}\)
Giải các pt sau:
a) \(\sin\left(3x+60^o\right)=\dfrac{1}{2}\)
b) \(\cos\left(2x-\dfrac{\pi}{3}\right)=\dfrac{-\sqrt{2}}{2}\)
c) \(\tan\left(x+\dfrac{\pi}{6}\right)=\sqrt{3}\)
d) \(\cot\left(2x+\pi\right)=-1\)
giải phương trình sau : a) \(\tan\frac{x}{2}=\tan x\) ; b) \(\tan\left(2x+10^o\right)+\cot x=0\) ; c) \(\left(1-\tan x\right)\left(1+\sin2x\right)=1+\tan x\) ; d) \(\tan x+\tan2x=\sin3x\cos x\) ; e) \(\tan x+\cot2x=2\cot4x\)
giải phương trình sau : a) \(\tan\frac{x}{2}=\tan x\) ; b) \(\tan\left(2x+10^o\right)+\cot x=0\) ; c) \(\left(1-\tan x\right)\left(1+\sin2x\right)=1+\tan x\) ; d) \(\tan x+\tan2x=\sin3x\cos x\) ; e) \(\tan x+\cot2x=2\cot4x\)
Giải các phương trình sau:
a) \(2sin\left(x+\dfrac{\pi}{5}\right)+\sqrt{3}=0\)
b)\(sin\left(2x-50\text{°}\right)=\dfrac{\sqrt{3}}{2}\)
c)\(\sqrt{3}tan\left(2x-\dfrac{\pi}{3}\right)-1=0\)
giải các phương trình sau : a) \(\tan3x=\tan\frac{3\pi}{5}\) ; b) \(\tan\left(x-15^o\right)=5\) ; c) \(\tan\left(2x-1\right)=\sqrt{3}\) ; d) \(\cot2x=\cot\left(-\frac{1}{3}\right)\) ; e) \(\cot\left(\frac{x}{4}+20^o\right)=-\sqrt{3}\) ; f) \(\cot3x=\tan\frac{2\pi}{5}\)
\(tan\left[\dfrac{\pi}{4}\left(cosx-sinx\right)\right]=1\)
