Question

Сократить дробь х^2+4х-21 дробная черта 3х-9

Answer 1

$\displaystyle \frac{ x^2+4x-21}{3x-9}= \frac{x^2+4x+4-25}{3x-9}= \frac{(x+2)^2-5^2}{3(x-3)} =\\ \\ \\ = \frac{(x+2-5)(x+2+5)}{3(x-3)} = \frac{(x-3)(x+7)}{3(x-3)}= \frac{x+7}{3}$