2.2 cm

3. Angle CAD CAD C (ASA)

4. Solution: In △COA and △BOA.

∠ A =∠ D (known)

∠COA=∠BOD (equal to vertex angle)

CO=BO (known)

∴△COA≡△BOA(AAS)

∴AO=DO

5.( 1)∠DEB =∠DCB∠CBD =∠EBD∠ADE =∠BDE

(2) straight line AE=BE DE=DC EB=CB.

(3)△EDB and △CDB △ADE and △BDE

6. Sketch: The vertical scales of of OF⊥DE OG⊥AE OH⊥AD are f g h respectively.

∫ DC bisection ∠ Ade ∴OH=OF

Similarly, EB shares ∠AED ∴OF=OG.

∴OH=OF=OG

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