#include <algorithm>
#include <cstdio>
#define debug(...) fprintf(stderr, __VA_ARGS__)

using i64 = long long;

inline i64 rd() {
	i64 x = 0, f = 1, c = getchar();
	while (((c - '0') | ('9' - c)) < 0)
		f = c != '-', c = getchar();
	while (((c - '0') | ('9' - c)) > 0)
		x = x * 10 + c - '0', c = getchar();
	return f ? x : -x;
}

const int N = 2e5;

int n, k;
i64 X[N + 5], Y[N + 5];

inline i64 cross(int i, int j) {
	return X[i] * Y[j] - X[j] * Y[i];
}

void solve() {
	n = rd(), k = rd();
	for (int i = 0; i < n; i++) X[i] = rd(), Y[i] = rd();

	i64 S = 0;
	for (int i = 0; i < n; i++) S += cross(i, (i + 1) % n);
	// debug("[S] %lld\n", S);

	i64 Sbc = 0;
	for (int i = 0; i < k; i++) Sbc += cross(i, i + 1);

	static int q[N + 5];
	int hd = 1, tl = 0;
	for (int i = k; i < n; i++) q[++tl] = i;

	i64 ans = 0;
	for (int i = 0; i < n; i++) {
		// debug(">>>>>>>>>> b = %d <<<<<<<<<<\n", i);
		int j = (i + k) % n;

		auto calc = [&](int p) -> i64 {
			// debug("calc(%d) = %lld\n", p, cross(q[p], i) + cross(i, j) + cross(j, q[p]));
			return cross(q[p], i) + cross(i, j) + cross(j, q[p]);
		};

		int l = hd, r = tl + 1;
		while (l + 2 < r) {
			int m1 = (l + r) / 2, m2 = m1 + 1;
			if (calc(m1) < calc(m2)) l = m1;
			else r = m2;
		}
		i64 mx = 0;
		for (int p = std::max(hd, l - 3), lp = std::min(tl, r + 3); p <= lp; p++) {
			mx = std::max(mx, calc(p));
		}
		ans = std::max(ans, mx + Sbc + cross(j, i));

		Sbc -= cross(i, (i + 1) % n);
		Sbc += cross(j, (j + 1) % n);
		hd++, q[++tl] = i;
	}

	printf("%.15lf\n", ans * 0.5);
}

int main() {
	for (int T = rd(); T; T--) solve();
	return 0;
}