Bonjour,
Factoriser C2:
C2= 4 -49x²+(7x-2)(8x-2)
= (2-7x)(2+7x) + (7x-2)(8x-2)
= (-7x+2)(7x+2) + (7x-2)(8x-2)
= -(7x-2)(7x+2) +(7x-2)(8x-2)
= (7x-2)(-(7x+2)+(8x-2))
= (7x-2)(-7x-2+8x-2)
= (7x-2)(x-4)
Vérification :
(7x-2)(x-4) = 7x² - 28x - 2x + 8 = 7x² - 30x +8
4 -49x²+(7x-2)(8x-2) = 4 - 49x² + 56x² - 14x - 16x + 4 = 7x² - 30x + 8
On obtient bien la même chose.
