Solution: rotate the triangle ABD around point A by 90 to make AB and AC coincide. The new symbol for point d is e.

Link DE

∠∠DAE =∠BAC = 90

∴AD？ +AE？ (AE=AD)=DE？ =4

∴DE=2

∵EC？ (EC=BD)+ED？ =CD？

∴∠CED=90

CE = 2DE

∴∠ECD=30

∴∠CDE=60

∠ ade = 45 (AD = AE ∠ DAE = 90)

∴∠ADC= 105

Thank you very much