Đáp án:
5) \(x = - \dfrac{{15}}{2}\)
Giải thích các bước giải:
\(\begin{array}{l}
1)25{x^2} + 10x + 1 - 25{x^2} + 9 = 30\\
\to 10x = 20\\
\to x = 2\\
2)x\left( {{x^2} - 25} \right) - \left( {{x^3} + {2^3}} \right) = 17\\
\to {x^3} - 25x - {x^3} - 8 = 17\\
\to - 25x = 25\\
\to x = - 1\\
3)5x\left( {{x^2} - 6x + 9} \right) - 5\left( {{x^3} - 3{x^2} + 3x - 1} \right) + 15\left( {{x^2} - 16} \right) = 5\\
\to 5{x^3} - 30{x^2} + 45x - 5{x^3} + 15{x^2} - 15x + 5 + 15{x^2} - 240 = 5\\
\to 30x = 240\\
\to x = 8\\
4){x^2} + 8x + 16 - {x^2} + 1 = 16\\
\to 8x = - 1\\
\to x = - \dfrac{1}{8}\\
5)4{x^2} - 4x + 1 + {x^2} + 6x + 9 - 5\left( {{x^2} - 1} \right) = 0\\
\to 5{x^2} + 2x + 10 - 5{x^2} + 5 = 0\\
\to 2x = - 15\\
\to x = - \dfrac{{15}}{2}
\end{array}\)
