Tìm x biết: 25(x + 3)^2 + (1-5x)(1 + 5x) = 8

\[25{\left( {x + 3} \right)^2} + \left( {1-5x} \right)\left( {1 + 5x} \right) = 8\]

\(25\left( {{x^2} + 6x + 9} \right) + \left[ {{1^2} - {{\left( {5x} \right)}^2}} \right] = 8\)

\[25{x^2} + 150x + 225 + 1 - 25{x^2} = 8\]

\[150x = - 218\]

\(x = - \frac{{109}}{{75}}.\)

Vậy \(x = - \frac{{109}}{{75}}.\)