Phương trình \(\tan x+\tan \left(x+\frac{\pi}{3}\right)+\tan \left(x+\frac{2 \pi}{3}\right)=3 \sqrt{3}\) tương đương với phương trình:
Hãy suy nghĩ và trả lời câu hỏi trước khi xem đáp án
Lời giải:
Báo sai\(\tan x+\tan \left(x+\frac{\pi}{3}\right)+\tan \left(x+\frac{2 \pi}{3}\right)=3 \sqrt{3}\Leftrightarrow \tan x+\frac{\tan x+\tan \frac{\pi}{3}}{1-\tan x \tan \frac{\pi}{3}}+\frac{\tan x+\tan \frac{2 \pi}{3}}{1-\tan x \tan \frac{2 \pi}{3}}=3 \sqrt{3} \Leftrightarrow \tan x+\frac{\tan x+\sqrt{3}}{1-\sqrt{3} \tan x}+\frac{\tan x-\sqrt{3}}{1+\sqrt{3} \tan x}=3 \sqrt{3}\)
\(\begin{array}{l} \Leftrightarrow \frac{\tan x\left(1-3 \tan ^{2} x\right)+(\tan x+\sqrt{3})(1+\sqrt{3} \tan x)+(\tan x-\sqrt{3})(1-\sqrt{3} \tan x)}{1-3 \tan ^{2} x}=3 \sqrt{3} \\ \Leftrightarrow \frac{\tan x-3 \tan ^{3} x+\tan x+\sqrt{3} \tan ^{2} x+\sqrt{3}+3 \tan x+\tan x-\sqrt{3} \tan ^{2} x-\sqrt{3}+3 \tan x}{1-3 \tan ^{2} x}=3 \sqrt{3} \\ \Leftrightarrow \frac{9 \tan x-3 \tan ^{3} x}{1-3 \tan ^{2} x}=3 \sqrt{3} \Leftrightarrow \frac{3 \tan x-\tan ^{3} x}{1-3 \tan ^{2} x}=\sqrt{3} \Leftrightarrow \tan 3 x=\sqrt{3} \end{array}\)