Réponse:
5x^2+7x+(8x^2-3x)
= 5x^2+7x+8x^2-3x
= 13x^2+4x
Bsr
= 5x²+7x+(8x²-3x)
= 5x²+7x+8x²-3x
= 13x²+7x-3x
= 13x²+4x
Voilà !