uva 10014(数学)

题解：从递推公式中找到规律，a1 = (a - C + n * a0) / (n + 1)  其中a是a_n+1，C是2 * n *c1 +  2 * (n - 1) * c2 + ... + 2 * cn 。

#include <iostream>
#include <cstdio>
using namespace std;
const int N = 3005;

int main() {
	double a0, c[N], C, a, ans;
	int cases, n;
	scanf("%d", &cases);
	while (cases--) {
		C = ans = 0;
		scanf("%d", &n);
		scanf("%lf%lf", &a0, &a);
		for (int i = 1, j = n; i <= n; i++, j--) {
			scanf("%lf", &c[i]);
			c[i] = 2 * c[i] * j;
			C += c[i];
		}
		ans = (a - C + n * a0) / (n + 1);
		printf("%.2lf\n", ans);
		if (cases)
			printf("\n");
	}
	return 0;
}