Question

已知;在△ABC中,AB=AC,D是BC上一点,E是AC上一点,AD=AE,∠BAD=30°,求∠EDC的度数

Answer 1

AB=AC,∠B=∠C=(180°-∠BAC)/2=(150°-∠DAC)/2,

∠ADC=∠B+∠BAD=(150°-∠DAC)/2+30°=(210°-∠DAC)/2,

AD=AE,∠ADE=(180°-∠DAC)/2,

∠EDC=∠ADC-∠ADE=(210°-∠DAC)/2-(180°-∠DAC)/2=15°.