A) Aire MDC : (MD*DC)/2 = [(6-x)*6]/2 = (36-6x)/2 = -3x+18 cm²
Aire NBC : (NB*BC)/2 = [(6-x)*6]/2 = -3x+18 cm²
B) Aire AMCN = Aire ABCD - ( Aire MDC + Aire NBC )
= 6*6 - 2*(-3x+18)
= 36+6x-36
= 6x cm²
C) Pour x = 2
Aire MDC et NBC = -3x+18 = -3*2+18 = -6+18 = 12 cm²
Aire AMCN = 6x = 6*2 = 12 cm²