不知道写啥

解题思路:把分母和分子拆开看

注意事项:保留小数点后两位，注意定义类型

参考代码:

#include<iostream>

#include<cmath>

#include<iomanip>

using namespace std;

double ab(double i)//分子数列

{

double sum = 0;

if (i == 1)

{

return 2;

}

if (i == 2)

{

return 3;

}

sum = ab(i - 1) + ab(i - 2);

return sum;

}

double bc(double m)//分母数列

{

double sum = 0;

if (m == 1)

{

return 1;

}

if (m == 2)

{

return 2;

}

sum = bc(m- 1) + bc(m - 2);

return sum;

}

double sum(double m)

{

double sum = 0;

for (int i = 1; i < m + 1; i++)数列比之和

{

double abc = ab(i) / bc(i);

sum = sum + abc;

}

return sum;

}

int main()

{

double N;

cin >> N;

cout <<setprecision(2)<<fixed<<sum(N);

}