1/2 )+(1/3+1/5+...+1/49)-(1/4+1/6+1/8+……1/50)]/(1/26+1/27+...+1/50)=[1/2+(1/3+1/5+...+1/49)-1/2*(1/2+1/3+1/4+……1/25)]/(1/26+1/27+.....
1-1/2+1/3-1/4+1/5-1/6+1/7-1/8+1/9-1/10+……+1/49-1/50
=1+1/2+1/3+……+1/50-2*(1/2+1/4+1/6+……+1/50)
=1+1/2+1/3+……+1/50-(1+1/2+1/3+……+1/25)
=1/26+1/27+1/28+……+1/50