Stiind ca Abm e unghi exterior la abc
==> ABC + ABM = 180*
Inlocuim
Abc=180 grade - 120 grade
Abc = 60*
==> ACB + ACN = 180*
Inlocuim
ACB=180 grade - 130 grade
ACB = 50*
==> A+B+C = 180*
==> A+50+60 GRADE = 180* /-110
A=70*
Raspunsuri: A=70 grade
B= 60 grade
C= 50 grade
