Réponse:
A=2(x^2+x-1)
B=-(25+20x+4x^2)
C=49-x^2-(x+7)(2x-3)
(7-x)(7+x)-(x+7)(2x-3)
( x+7)[(x-7)-(2x-3)]
(x-7)(x-7-2x+3)
(x-7)(-x-5)
