4000 2017 ACM-ICPC 亚洲区（西安赛区）网络赛 B. Coin

#include <iostream>
#include <string>
#include <vector>
#include <stack>
#include <queue>
#include <deque>
#include <set>
#include <map>
#include <algorithm>
#include <functional>
#include <utility>
#include <cstring>
#include <cstdio>
#include <cstdlib>
#include <ctime>
#include <cmath>
#include <cctype>
#define CLEAR(a, b) memset(a, b, sizeof(a))
#define IN() freopen("in.txt", "r", stdin)
#define OUT() freopen("out.txt", "w", stdout)
#define LL long long
#define maxn 10000005
#define maxm 100005
#define mod 1000000007
#define INF 1000000007
#define EPS 1e-7
#define PI 3.1415926535898
#define N 26
using namespace std;
//-------------------------CHC------------------------------//
LL qpow(LL a, LL b) {
int ret = 1;
while (b) {
if (b & 1) ret = ret * a %mod;
a = a*a%mod;
b >>= 1;
}
return ret;
}

int main() {
int T;
cin >> T;
while (T--) {
int a, b, k;
cin >> a >> b >> k;
LL ans = (qpow(a - 2 * b, k)*qpow(qpow(a, k), mod - 2)%mod + 1)*qpow(2, mod - 2)%mod;
cout << ans << endl;
}
return 0;
}