Cách 1: \(3x^2-5x-22=3x^2-11x+6x-22\)
\(=x\left(3x-11\right)+2\left(3x-11\right)\)
=(3x-11)(x+2)
Cách 2:
\(3x^2-5x-22\)
\(=3\left(x^2-\dfrac{5}{3}x-\dfrac{22}{3}\right)\)
\(=3\left(x^2-2\cdot x\cdot\dfrac{5}{6}+\dfrac{25}{36}-\dfrac{289}{36}\right)\)
\(=3\left[\left(x-\dfrac{5}{6}\right)^2-\left(\dfrac{17}{6}\right)^2\right]\)
\(=3\left(x-\dfrac{5}{6}-\dfrac{17}{6}\right)\left(x-\dfrac{5}{6}+\dfrac{17}{6}\right)\)
\(=3\left(x-\dfrac{22}{6}\right)\left(x+\dfrac{12}{6}\right)=3\left(x+2\right)\left(x-\dfrac{11}{3}\right)\)
Đúng 3
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