Réponse:
a²-b²=(a-b)(a+b)
(x²-25)-2(5-x)(x+6) =
((x-5)×(x+5))-2×(-(x-5))×(x+6)
(x-5)×(x+5)+2(x-5)×(x+6)
(x-5)×(x+5+2(x+6))
(x-5)×(x+5+2x+12)
(x-5)×(3x+17)
