Daca unghiul format de bisectoare este 130=a+b, a=m<ABC/2, b=m<CBD/2
m < ABD=360 grade - (m< ABC+m<CBD)=360 grade- 2*130=360-260= 100 grade
m<ABD/2=50 grade
50+40+<ABC=180 grade
90+<ABC=180 grade
rezulta <ABC=90 grade,
< ABC+<BCD=360-100 grade=260 grade
<BCD=260-90=170 grade