Bonsoir,
a) 7y - (3a + 2V)(3a - 2y)
7y -(9a²-6ay + 6Va - 4Vy)
= 7y- 9a²+6ay - 6Va + 4Vy
b) (- f + 5) (3 - 5t)
= -3f +5ft +15 -25t
c)(a + b)(4b - 2a) (a + 2)
= (4ab -2a² +4b² -2ab) ( a+2)
= 4a²b +8ab - 2a³ - 4a² +4ab² + 8b² -2a²b - 4ab
= -2a³+2a²b +4ab² -4a² +8b²+4ab
Bsr
A = 7y-(3a+2V)(3a - 2y)
A = 7y-(9a²-6ay+6Va-4Vy)
A = 7y-9a²+6ay-6Va+4Vy
B = (- f + 5)(3 - 5t)
B = -3f+5ft+15-25t
C = (a + b)(4b - 2a)(a + 2)
C = (4ab-2a² +4b²-2ab)(a+2)
C = 4a²b+8ab-2a³-4a²+4ab²+8b²-2a²b-4ab
C = -2a³+2a²b+4ab²-4a²+8b²+4ab
Voilà !