50×51/1+51×52/1+52×53/1+53×54/1+54×55/1分析：50×51/1=(51-50)/50×51=1/50-1/5151×52/1=(52-51)/ 51×52=1/51-1/5252×53/1=(53-52)/ 52×53=1/52-1/5353×54/1=(54-53)/53...