第1个回答 2010-07-26
①=1/(1×2)+1/(2×3)+1/(3×4)+…+1/(6×7)+1/(7×8)
=1-1/2+1/2-1/3+1/3-1/4+…+1/6-1/7+1/7-1/8
=7/8
②=5×[1/(2+5×1)+1/(2+5×3)+1/(2+5×5)+…+1/(2+5×31)]
然后通分,接着可以代掉,过程太麻烦了,故你自己去算
③=[(1+6)+(2+5)+(3+4)+…+(4+3)(5+2)(6+1)]/[(7×7)×(111111 ×111111)
=(7×7)/[(7×7)×(111111×111111)]
=1/(111111×111111)
=1/12345654321
我回答的更全采纳啊!!!!!!!!!!!!!!
第2个回答 2010-07-29
/2+1/6+1/12+1/20+1/30+1/42+1/56
=1/(1*2)+1/(2*3)+1/(3*4)+1/(4*5)+1/(5*6)+1/(6*7)+1/(7*8)
=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8
=1-1/8
=7/8
(5/1×6+4/6×11+5/11×6+…+5/76×81)/(5/4)=(1-1/6+1/6-1/11+1/11…+1/76-1/81)/(5/4)=(1-1/81)*(4/5)=64/81
第4个回答 2010-08-02
(1).1/2+1/6+1/12+1/20+1/30+1/42+1/56=1-1/2+1/2-1/3+1/3......+1/7-1/8=7/8
(2) .5/(1+6)+5/(6+11)+5/(11+16)+……+5/(76+81)=2
(3). (1+2+3+4+5+6+7+6+5+4+3+2+1)/(777777*777777)=0.000000000081000162000243
第5个回答 2010-08-05
天啊,我是高级工程师啊,居然都不会。虽然当年数学差了点,但也不至于差这么多啊!!!!!现在的孩子怎么活啊???????