程序代码：

6.
#include <stdio.h>

double func(double x)
{
    return x*x - 6.5*x + 2;
}

void main()
{
    double x = -3;
    printf("     x\t     y\n");
    
    for (int i = 0; i < 13; i++)
    {
        printf("%6.2lf\t%6.2lf\n", x, func(x));
        x += 0.5;
    }

    return;
}

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7.
#include<stdio.h>

int func(int x, int y)
{
    return x*x + y*y;
}

int main()
{
    int S = 0;
    for (int i = 1; i < 30; i++)
    {
        S += func(i, i + 1);
    }

    printf("%d", S);
    
    return 0;
}

-----------------------------------------------------------------------------
8.
#include <stdio.h>

double f(int n)
{
    double s = 0;
    for (int i = 0, j = 0; i < 2*n-1-n+1; i++,j++)
    {
        s += n + j;
    }
    return s;
}

int main()
{
    int n;
    double S = 0;
    scanf("%d", &n);
    for (int i = 1; i <= n; i++)
    {
        S += f(i) / i;
    }

    printf("%lf", S);
    
    return 0;
}