64x²-9+(7x-2)(8x+3)
= 64x²-9 +(56x²+21x-16x-6)
= 64x²-9+56x²+21x-16x-6
= 120x² +5x -15
64x²-9 = (8x-3)(8x+3) identité remarquable
(8x+3)(8x-3)+(7x-2)
= (8x+3)(8x-3+7x-2)
= (8x+3)(15x-5)
(8x-3)(15x-5 )= 0 admet 2 solutions
ou 8x-3 = 0 donc 8x=3 et x = 3/8
ou 15x-5 = 0 donc 15x=5 d'où x = 5/15 ou 1/3
