Bonjour

D =  ( - 7 x + 6 ) ( 5 - x²)

D =  - 35 x + 7 x ³ + 30 - 6 x²

Bsr

D = (-7x+6)(5-x²)

D = -7x×5-7x×(-x²)+6×5-6x²

D = -35x-7x×(-x²)+6×5-6x²

D = -35x+7x×x²+6×5-6x²

D = -35x+7x³+6×5-6x²

D = -35x+7x³+30-6x²

Voilà !