Bjr,
a) aire de MDC = (MD * DC) / 2
= ((6-x)*6) / 2
= (36 - 6x) / 2
= 18 - 3x
aire de NBC = aire de MDC
b) aire de AMCN = aire de ABCD - (aire de MDC + aire de NBC)
= 6*6 - ( 2 * (18-3x))
= 36 - (36 - 6x)
= 36 - 36 + 6x
= 6x
c) si x=2
aire de MDC = aire de NBC = 18 - 3*2 = 18 - 6 = 12
aire de AMCN = 6x = 6*2 = 12