Question

如图所示,∠B＝45°,∠A＝30°,∠C＝25°.求∠ADC的大小.

Answer 1

连接BD并延长到E,

则∠CDE=∠DBC+∠C

∠ADE=∠DBA+∠A

∴∠ADC=∠CDE+∠ADE

=∠DBC+∠C+∠DBA+∠A

=∠CBA+∠C+∠A

=45°+30°+25°=100°