問功課最好係返功課討論區問 XD

第1幅圖
a. (2x-10°)+98° = 180° (adj.∠s on st.line)
             2x-10° = 82°
                     x = 46°
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b. Ref. to the fig.
    ∵ MF // BA (by construction)
    ∠BEF = ∠ABE = 40° (alt.∠s, MF // BA)
    ∠DEF = 180° - 40° - 98° (adj.∠s on st. line)
             =∠CDE
    ∴ MF // CD // AB (alt.∠s equal)

第3幅圖
∠FDM = ∠EMC (alt.∠s, DF//AM)
∠DEF = ∠CEM (vert. opp. ∠s)
∠ABC = ∠ACB (base ∠s, isos.△)
∠DFB = ∠ACB (corr. ∠s, DF // AC)
∠DFB = ∠ABC
DB = DF = CM (sides opp. equal ∠s)
∴ △DEF is congruent to △MEC (AAS)
∴ DE=EM (corr.sides, congruent △s)

希望無錯,可以幫到你

[ 本帖最後由 tantc 於 2007-9-1 03:11 PM 編輯 ]

sell post deleted, thanks a lot

[ 本帖最後由 tantc 於 2007-9-1 07:29 PM 編輯 ]