大虾进来救救急!第一题:1/2+1/6+1/12+1/20+1/30+1/42+1/56第二题:498*381+382/

第一题:1/2+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
第二题
498*381+498-116
= ——————————
498*381+382
498*381*（498-116）
= ——————————
498*381+382
498*381+382
= ——————————
498*381+382
=1

1/2+1/6+1/12+1/20+1/30+1/42+1/56=1/(1*2)+1/(2*3)+...+1/(6*7)+1/(7*8)=1-1*8=7/8
498*381+382/382*498-116=190120（是不是丢了括号之类的）

=0.875(7/8)
≈189622.002