Ex. 3:
15x³-7x²-2x = x(3x-2)(5x+1)
⇒ 15x³-7x²-2x = x(15x²+3x-10x-2)
⇒ 15x³-7x²-2x = x(15x²-7x-2)
⇒ 15x³-7x²-2x = 15x³-7x²-2x
⇒ 15x²-15x³-7x²+7x²-2x+2x = 0
⇒ 0 = 0
pas de solution
Ex. 4 :
x²-y² = (x+y)(x-y)
si x+y = 4 et x²-y² = 48
alors, 4(x-y) = 48
donc, (x-y) = 48/4 = 12
donc, (x-y)² = 12² = 144