Triunghiul AEC dreptunghi
A=90 grade
C=40 grade =>AEC=50 grade=>AEC=DEB(unghiuri opuse la vârf)
=>x+BEC=360 grade-AEC-DEB=> x+BEC=260 grade=>x=130 grade BEC=130 grade(unghiuri opuse la vârf)=>x=130 grade
Triunghiul BED dreptunghic
B=90 grade
E=50 grade => D=40 grade=>x=D=40 grade
x+y=130 grade+ 40 grade=170 grade(b)