一百分之一加一百分之三加一百分之五……加一百分之九十九
=(1/100+99/100)×50/2
=50/2
=25
一百分之一加一百分之三加一百分之五……加一百分之九十九
=(1/100+99/100)+(3/100+97/100)+(49/100+51/100)
=1+1+...+1
=25
一百分之一加一百分之三加一百分之五……加一百分之九十九
=1/100x(1+3+...+99)
=1/100x(1+99)x50÷2
=1/100x100x25
=25
分子是一个等差数列,公差为2,等差数列求和就好了!