第1个回答 2010-09-27
设A=1/2+1/3+1/4,B=1/2+1/3+1/4+1/5
原式=(1+A)×B-(1+B)×A=B+A×B-A-A×B=B-A=1/2+1/3+1/4+1/5-(1/2+1/3+1/4)=1/5
第2个回答 2010-09-27
原式变为(1+1/2+1/3+1/4)*(1/2+1/3+1/4+1/5)-(1+1/2+1/3+1/4+1/5)*(1+1/2+1/3+1/4)+(1+1/2+1/3+1/4+1/5)
=(1+1/2+1/3+1/4)*(1/2+1/3+1/4+1/5-1-1/2-1/3-1/4-1/5)+(1+1/2+1/3+1/4+1/5)
=(1+1/2+1/3+1/4)*(-1)+(1+1/2+1/3+1/4+1/5)
=1/5
第3个回答 2010-09-27
结果为1/5
把1/2+1/3+1/4看作一个整体,用△表示
为(1+△)×(△+1/5)-(1+△+1/5)×△
=△²+6/5△+1/5-(△²+6/5△)
=1/5