Răspuns :
<FOE= 90⁰
<DOE= 30⁰
EO mijlocul lui DOC
=> <EOC=30⁰
<DOC= <DOE+<EOC=30⁰+30⁰=60⁰
<FOE=90⁰
<DOE=30⁰
=> <FOD= <FOE- <DOE
=> <FOD= 90⁰-30⁰
=> <FOD=60⁰
FO mijlocul lui AOD
=> <AOF=<FOD=60⁰
<AOD=<AOF+<FOD=60⁰+60⁰=120⁰
<AOC=180⁰
<BOD=180⁰
<AOB=<DOC=60⁰
<BOC=<AOD=120⁰