Bonjour,
a) A(x) = aire AEFG = AE × GA
AE = AB - EB = AB - 2GD = 16 - 2x
GA = AD - DG = 8 - x
donc A(x) = (16 - 2x)(8 - x)
b) A(x) = (16 - 2x)(8 - x) = 16×8 - 16x - 16x + 2x²
= 2x² - 32x + 128
c) A(x) = 2x² - 32x + 128 = 2(x² - 16x + 64) = 2(x - 8)²
d) pour calculer A(4), l'écriture la plus adaptée est A(x) = 2(8 - x)²
A(4) = 2(8-4)² = 2(4²) = 32