Réponses

2013-11-27T10:38:19+01:00
Bonjour

3x² - 9x - 30 = 0

a = 3 ; b = -9 ; c = -30

Discriminant : \Delta = b^2-4ac= (-9)^2-4\times3\times(-30)=81+360=441

Solutions : 

x_1=\dfrac{-(-9)-\sqrt{441}}{2\times3}=\dfrac{9-21}{6}=\dfrac{-12}{6}=-2\\\\x_2=\dfrac{-(-9)+\sqrt{441}}{2\times3}=\dfrac{9+21}{6}=\dfrac{30}{6}=5

Factorisation :  3x² - 9x - 30 = 0 ==> 3(x + 2)(x - 5) = 0