Question

已知在三角形ABC中,AB=AC,D是BC上一点,角BAD=30°,E是AC上一点,且AD=AE,求角EDC的度数.

Answer 1

∠EDC=180°-∠CED-∠C

=180°-∠ADE-∠DAE-∠C

=180°-(180°-∠DAE)/2 - ∠DAE-∠C

=90°-∠DAE/2 - ∠C

=90°-(180°-2∠C-30°)/2 - ∠C

=∠C+15° - ∠C

=15°