谁能算出这三道题?
1.(1+1/2+1/3+1/4)*(1/2+1/3+1/4+1/5)-(1+1/2+1/3+1/4+1/5)*(1/2+1/3+1/4)
2.1/2+(1/3+2/3)+(1/4+2/4+3/4)+(1/5+2/5+3/5+4/5)+...+(1/100+2/100+3/100+...+99/100)
3.1-5/6+7/12-9/20+11/30-13/42+15/52-17/72