Ta có: \(2x^2+9x-14\)
\(=2\left(x^2+\frac92x-7\right)\)
\(=2\left(x^2+2\cdot x\cdot\frac94+\frac{81}{16}-\frac{193}{16}\right)\)
\(=2\left\lbrack\left(x+\frac94\right)^2-\frac{193}{16}\right\rbrack=2\left(x+\frac{9-\sqrt{193}}{4}\right)\left(x+\frac{9+\sqrt{193}}{4}\right)\)