地老天荒到永远
幼苗
共回答了15个问题采纳率:93.3% 举报
∵O为内心 ,∴∠DAB=∠DAC,∴弧BD=弧CD,∴BD=CD,
∵∠DBI=∠DBC+∠IBC=∠DAC+1/2∠ABC=1/2(∠BAC+∠ABC),
∠DIB=∠IBA+∠IAB=1/2(∠ABC+∠BAC),
∴∠DBI=∠DIB,∴BD=DI,
∴BD=DI=CD.
⑴∠BIC=∠DIB+∠DIC
=1/2∠ABC+1/2∠ABC+1/2∠ACB+1/2∠BAC
=1/2(∠ABC+∠BAC+∠ABC)+1/2∠BAC
=90°+1/2∠BAC
=112°.
1年前
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