pt $\Leftrightarrow \bigg (\dfrac{4-\sqrt 7}{3} \bigg )^x +\bigg (\dfrac{4+\sqrt 7}{3} \bigg )^x -\dfrac{5}{2}=0$
Đặt $\bigg (\dfrac{4-\sqrt 7}{3} \bigg )^x= t \Rightarrow \bigg (\dfrac{4+\sqrt 7}{3} \bigg )^x =\dfrac{1}{t}$
Pt $\Leftrightarrow t+\dfrac{1}{t} -\dfrac{5}{2}=0$
$\Leftrightarrow t^2 - \dfrac{5}{2}t+1=0$
$\Leftrightarrow t= 2;\ t=\dfrac{1}{2}$ coi như xong nhe