Tìm x , biết: d) 25 ( x + 3 ) ^2 + ( 1 − 5 x ) ( 1 + 5 x ) = 8.
Giải thích
d) \[25{\left( {x + 3} \right)^2} + \left( {1-5x} \right)\left( {1 + 5x} \right) = 8\]
\(25\left( {{x^2} + 6x + 9} \right) + \left[ {{1^2} - {{\left( {5x} \right)}^2}} \right] = 8\)
\[25{x^2} + 150x + 225 + 1 - 25{x^2} = 8\]
\[150x = - 218\]
\(x = - \frac{{109}}{{75}}.\)
Vậy \(x = - \frac{{109}}{{75}}.\)