A B
D C
m(A ) = m(D ) = 90
m(A) + m(B) + m(C ) + m(D ) = 360⁰
↓ ↓
90 90
m(B) + m(C) = 360⁰ - 90⁰ - 90⁰ = 180⁰
m(B ) -m ( C) = 38⁰ cele doua relatii adunate :
------------------------------------------
m(B) + m(B) = 180⁰ + 38⁰ = 218⁰ ; m(B) = 218⁰ :2 = 109⁰
m(C) = 109⁰ - 38⁰ = 71⁰