a: Ta có: AB\(\perp\)BC
DC\(\perp\)BC
Do đó: AB//DC
=>\(\widehat{BAI}+\widehat{AIC}=180^0\)(hai góc trong cùng phía)
=>\(\widehat{AIC}=180^0-45^0=135^0\)
b: Ta có: DC\(\perp\)DE
EF\(\perp\)DE
Do đó: DC//EF
Ta có: AB//DC
DC//EF
Do đó: AB//EF
c: Ta có: AB//DC
=>\(\widehat{IAB}=\widehat{AID}\)(hai góc so le trong)
=>\(\widehat{AID}=45^0\)
Ta có: DC//EF
=>\(\widehat{AID}=\widehat{IFE}\)(hai góc đồng vị)
=>\(\widehat{IFE}=45^0\)
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