Réponse:
Bjr, supprimons les parenthèses.
A=7-(2-a)+9+(b-5)
=7-2+a+9+b-5
= a+b+7+9-2-5
A= a+b+9.
B=15+(7-b)-9-(a-17)
= 15+7-b-9-a+17
= -a-b+22+17-9
B=30-a-b.
C=9-(c+4)-(3-b)+21-(17-c)
= 9-c-4-3+b+21-17+c
= b+9+21-7-17
C=b+6.
D=5×2-(3x-2)+(7x²-6)
= 10-3x+2+7x²-6
= 7x²-3x+10+2-6
D=7x²-3x+6.
