Tìm \(x,\) biết: \[{x^3} + 9{x^2} + 27x + 19 = 0;\]

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

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

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

\[150x = - 218\]

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

) \(\left( {x + 3y} \right)\left( {x - 2y} \right) - \left( {{x^4}y - 6{x^2}{y^3}} \right):{x^2}y\)

\( = {x^2} - 2xy + 3xy - 6{y^2} - \left( {{x^2} - 6{y^2}} \right)\)

\( = {x^2} + xy - 6{y^2} - {x^2} + 6{y^2}\)

\( = xy\).