Nguyễn Phong's Profile

`e^x-e^{-x}=0`

`\Leftrightarrow e^x-1/(e^{x})=0`

Đặt `e^x=t\ (t > 0)`

`\Leftrightarrow t-1/t=0`

`\Leftrightarrow t^2-1=0`

`\Leftrightarrow (t-1)(t+1)=0`

`\Leftrightarrow` \(\left[ \begin{array}{l}t=1\ (TM)\\t=-1\ (L)\end{array} \right.\) 

`t=1 -> e^x=1 \Leftrightarrow x=0`