100-99+98-97+...+6-5+4-3+2-1
=(100-99)+(98-97)+(96-95)+……+(6-5)+(4-3)+(2-1)
=1×50
=50
1/2+1/6+1/12+1/20+1/30+.+1/72+1/90
= 1/1*2 +1/2*3 +1/3*4 +...+1/8*9 +1/9*10
= (1/1 -1/2)+(1/2 -1/3)+...+(1/8 -1/9)+(1/9 -1/10)
= 1/1 -1/10
= 9/10
很高兴能帮到你,如果觉得好请选为满意答案 ,祝你学习进步 (*^__^*)