证明：因为∠C=90°,∠B=45° 则AC = ABsin45 因为AD平分∠BAC交BC于D 则CD = AC/tan22.5 = ABsin45/tan22.5 = 2AB(cos22.5)^2 则AC+CD = (sin45+2(cos22.5)^2)AB =(sin45+1-cos45)AB =AB 得证
