数学有疑问1、1/1*7+1/7*13+1/13*19+……+1/79*85=…………………………2、1/2+1/6+1/12+1/20+1/30+……+1/90=…………………………3、3又4/5*0.375+3.8/8+1/2除5/19=…………………………快

Question

数学有疑问 1、 1/1*7+1/7*13+1/13*19+……+1/79*85
=…………………………
2、 1/2+1/6+1/12+1/20+1/30+……+1/90
=…………………………
3、3又4/5*0.375+3.8/8+1/2除5/19
=………………………… 快

Answer 1

1.(1-1/7+1/7-1/13+1/13-1/19.+1/79-1/85)/6
=(1-1/85)/6
=14/85
2.1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+.+1/9-1/10
=1-1/10
=9/10
3.3.8*3/8+3.8/8+1/2*19/5
=3.8*(3+1+4)/8
=3.8
lz谢谢,分