Tìm x: $9{\left( {x + 1} \right)^2} - \left( {3x - 2} \right)\left( {3x + 2} \right) = 10$

Ta có : $9{\left( {x + 1} \right)^2} - \left( {3x - 2} \right)\left( {3x + 2} \right) = 10$

$\Leftrightarrow 9\left( {{x^2} + 2x + 1} \right) - \left( {9{x^2} - 4} \right) = 10$

$\Leftrightarrow 9{x^{2\;}} + 18x + 9 - 9{x^2} + 4 = 10$

$\Leftrightarrow 9{x^2} - 9{x^2} + 18x + 13 = 10$

$\Leftrightarrow 18x = 10 - 13$

$\Leftrightarrow 18x = - 3\;$

$\Leftrightarrow x = - \frac{1}{6}$.