A ABCD = BC * CD
BC * CD = 120
M -mijloc BC⇒BM=MC =BC/2
N - mijloc CD⇒CN=ND = CD/2
A ΔMCN = CM*CM :2 = BC/2*CD/2 *1/2 = BC*CD/8=120:8=15cm²
A ΔAMB + A ΔADN =AB*BC/2*1/2 +AD*CD/2 *1/2 = AB*BC/4 + AD*CD/4=
=120/4+120/4=240/4=60cm²
A ABCD = A ΔAMB + A ΔADN + AΔMCN + AΔAMN
120 = 15+60+AΔAMN
AΔAMN = 120-75 = 45 cm²
