Réponse :
Explications étape par étape
1) 0<=< <= 7
A (MBC) = MC x AD /2
= (7-x) x 4 / 2
= (7-x) x 2
A (MBC) = 14 -2x
A (ABMD) = (B +b) x h /2
= (MD + AB) x AD /2
=( x+4)x4/2
= (x+4) x 2
A (ABMD) = 2x +8
2) A (ABMD) = 12
2x+8 = 12
2x +8 - 8 = 12 -8
2x = 4
x = 2
3) A(ABMD) = A (MBC)
2x+ 8 = 14 - 2x
2x + 2x = 14 -8
4x = 6
x = 6/4
x = 3/2
Aire = 2x3/2 + 8 = 11