Sagot :
a = (3x²+8)-(21+x²)
= 3x²+8-21-x²
= 2x²-13
b = 17x-(5x²+9-4x)
= 17x-5x²-9+4x
=-5x²+21x-9
c = (4x²+7x+21)-(x²+2x-13)
= 4x²+7x+21-x²-2x+13
= 3x²+5x+34
= 3x²+8-21-x²
= 2x²-13
b = 17x-(5x²+9-4x)
= 17x-5x²-9+4x
=-5x²+21x-9
c = (4x²+7x+21)-(x²+2x-13)
= 4x²+7x+21-x²-2x+13
= 3x²+5x+34
a) ok mais tu peux encore reduire
2x²-13
b) =17x-5x²-9+4x=21x-5x²-9
c)4x²+7x+21-x²-2x+13=3x²+5x+34
voila
2x²-13
b) =17x-5x²-9+4x=21x-5x²-9
c)4x²+7x+21-x²-2x+13=3x²+5x+34
voila