∵四边形ABCD中
∠A+∠B+∠C+∠D=360°
∴∠C+∠D=360°-∠A-∠B
∴1/2(∠C+∠D)=180°-1/2∠A -1/2∠B
∵AE平分∠BAD,BE平分∠ABC
∴∠AEB=180°-1/2∠A-1/2∠B
∴∠AEB=1/2(∠C+∠D)
∵四边形ABCD中
∠A+∠B+∠C+∠D=360°
∴∠C+∠D=360°-∠A-∠B
∴1/2(∠C+∠D)=180°-1/2∠A -1/2∠B
∵AE平分∠BAD,BE平分∠ABC
∴∠AEB=180°-1/2∠A-1/2∠B
∴∠AEB=1/2(∠C+∠D)