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222-9+11+12:2*14+14 = ? ( )

Toán Lớp 8: Giải phương trình: d) (x ^ 2 + 3x + 2)(2x + 3)(2x + 5) = 30

Toán Lớp 8: Giải phương trình: d) (x ^ 2 + 3x + 2)(2x + 3)(2x + 5) = 30

1. Giải đáp: $x = 0;x = – \dfrac{7}{2}$
$\begin{array}{l} d)\left( {{x^2} + 3x + 2} \right)\left( {2x + 3} \right)\left( {2x + 5} \right) = 30\\ \Leftrightarrow \left( {x + 1} \right)\left( {x + 2} \right)\left( {2x + 3} \right)\left( {2x + 5} \right) = 30\\ \Leftrightarrow \left( {x + 1} \right)\left( {2x + 5} \right)\left( {x + 2} \right)\left( {2x + 3} \right) = 30\\ \Leftrightarrow \left( {2{x^2} + 7x + 5} \right)\left( {2{x^2} + 7x + 6} \right) – 30 = 0\\ Dat:2{x^2} + 7x + 5 = a\\ \Leftrightarrow a.\left( {a + 1} \right) – 30 = 0\\ \Leftrightarrow {a^2} + a – 30 = 0\\ \Leftrightarrow {a^2} + 6a – 5a – 30 = 0\\ \Leftrightarrow \left( {a + 6} \right)\left( {a – 5} \right) = 0\\ \Leftrightarrow \left[ \begin{array}{l} a + 6 = 0\\ a – 5 = 0 \end{array} \right.\\ \Leftrightarrow \left[ \begin{array}{l} 2{x^2} + 7x + 5 + 6 = 0\\ 2{x^2} + 7x + 5 – 5 = 0 \end{array} \right.\\ \Leftrightarrow \left[ \begin{array}{l} 2{x^2} + 7x + 11 = 0\left( {vn} \right)\\ 2{x^2} + 7x = 0 \end{array} \right.\\ \Leftrightarrow \left[ \begin{array}{l} x = 0\\ x = – \dfrac{7}{2} \end{array} \right.\\ Vậy\,x = 0;x = – \dfrac{7}{2} \end{array}$