
(1)如上图,AB=BD,BD=CD
∵AB=BD,∠A=76°
∴∠BDA=76°
∵BD=CD
∴∠DBC=∠C=∠BDA÷2
∴∠C=76°÷2=38°

(2)如上图,BD=AD,BD=CD
∵AD=BD,∠A=76°
∴∠ADB=180°-76°×2=28°
∵BD=CD
∴∠C=∠DBC=∠ADB÷2=28°÷2=14°

(3)如上图,AB=AD,BD=CD
∵AB=AD,∠A=76°
∴∠ADB=(180°-76°)÷2=52°
∵BD=CD
∴∠C=∠ADB÷2=52°÷2=26°