Réponse:
1) (x+1)^2 -(x-1)^2=(x^2+2x+1)-(x^2-2x+1)
=x^2+2x+1-x^2+2x-1=4x
2)A=21^2-19^2=(20+1)^2-(20-1)^2=4×20=80
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Réponse:
1) (x+1)^2 -(x-1)^2=(x^2+2x+1)-(x^2-2x+1)
=x^2+2x+1-x^2+2x-1=4x
2)A=21^2-19^2=(20+1)^2-(20-1)^2=4×20=80