解?$： (1)$?如圖
?$(2)$?由題意，得?$∠1 = ∠2，$??$∠3 = ∠4，$??$∠5 = ∠6。$?
?$ $?又因為?$∠7 = ∠1 + ∠5，$??$∠8 = ∠3 + ∠6，$?
?$ $?所以?$∠7 + ∠8 = (∠1 + ∠3)+(∠5 + ∠6)$?
?$=\frac {1}{2}(∠ABC + ∠ACB)+∠BAC。$?
?$ $?因為?$∠ABC + ∠ACB=180°-∠BAC，$?
?$ $?所以?$\frac {1}{2}(∠ABC + ∠ACB)+∠BAC=\frac {1}{2}(180°-∠BAC)+∠BAC $?
?$= 90°+\frac {1}{2}∠BAC。$?
?$ $?已知?$∠BAC = 70°，$?
則?$90°+\frac {1}{2}×70°=90°+35°=125°，$?
即?$∠BOC = 125°。$?
