Question

初三数学题第（3、4）小题

Answer 1

3）
∵OM ⊥ AF ，ON ⊥ DF
∴∠OMF = ∠ONF = 90
ON = OM
∴△OMF ≌ △ONF
∠OFM = ∠OFN，MF = NF
2∠OFN = ∠OMN
--------------------------
FG平分∠DFE
2∠DFG = ∠DFE
∠AFE = ∠DFE + ∠OMN = 2（∠DFG + ∠OFN）=2∠OFG = 180
∠OFG = 90
OF⊥FG
--------------------
MF = NF = 1/2 AF = 1/2 DF（不证明了）
AF = DF
∠ADF = ∠DAF
∠ADF = 90 - ∠OFA = ∠DFG
AD∥FG

4）
AD∥FG
∠DAF = ∠GFE
∠ADF = ∠DFG
FG平分∠DFE
∠GFE = ∠DFG
∠DAF = ∠ADF
DF = AF
∵OM ⊥ AF ，ON ⊥ DF
2MF = AF，2NF = DF，∠OMF = ∠ONF = 90
∴△OMF ≌ △ONF
∴OM= ON

写得不是很详细，差的自己补下