Răspuns:
Explicație pas cu pas:
<BAM = <BMA = 45
BM = AB = CD
BM+MC +2AB + AD = 56
BM+MC = AD
BM +MC +2BM +BM+MC =56
4BM +2MC =56
Dar BM = 2/3MC
4*2/3MC +2MC = 56
8MC +6MC = 3*56
14MC =3*56
MC = 3*4 = 12
BM = 2*12/3 = 8
BC = 8 +12 = 20
