#pragma region satashun //#pragma GCC optimize("Ofast") //#pragma GCC optimize("unroll-loops") #include using namespace std; using uint = unsigned int; using ll = long long; using ull = unsigned long long; using pii = pair; template using V = vector; template using VV = V>; template V make_vec(size_t a) { return V(a); } template auto make_vec(size_t a, Ts... ts) { return V(ts...))>(a, make_vec(ts...)); } #define pb push_back #define eb emplace_back #define mp make_pair #define fi first #define se second #define rep(i, n) rep2(i, 0, n) #define rep2(i, m, n) for (int i = m; i < (n); i++) #define per(i, b) per2(i, 0, b) #define per2(i, a, b) for (int i = int(b) - 1; i >= int(a); i--) #define ALL(c) (c).begin(), (c).end() #define SZ(x) ((int)(x).size()) constexpr ll TEN(int n) { return (n == 0) ? 1 : 10 * TEN(n - 1); } template void chmin(T& t, const U& u) { if (t > u) t = u; } template void chmax(T& t, const U& u) { if (t < u) t = u; } template void mkuni(vector& v) { sort(ALL(v)); v.erase(unique(ALL(v)), end(v)); } template vector sort_by(const vector& v, bool increasing = true) { vector res(v.size()); iota(res.begin(), res.end(), 0); if (increasing) { stable_sort(res.begin(), res.end(), [&](int i, int j) { return v[i] < v[j]; }); } else { stable_sort(res.begin(), res.end(), [&](int i, int j) { return v[i] > v[j]; }); } return res; } template istream& operator>>(istream& is, pair& p) { is >> p.first >> p.second; return is; } template ostream& operator<<(ostream& os, const pair& p) { os << "(" << p.first << "," << p.second << ")"; return os; } template istream& operator>>(istream& is, vector& v) { for (auto& x : v) { is >> x; } return is; } template ostream& operator<<(ostream& os, const vector& v) { os << "{"; rep(i, v.size()) { if (i) os << ","; os << v[i]; } os << "}"; return os; } #ifdef LOCAL void debug_out() { cerr << endl; } template void debug_out(Head H, Tail... T) { cerr << " " << H; debug_out(T...); } #define debug(...) \ cerr << __LINE__ << " [" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__) #define dump(x) cerr << __LINE__ << " " << #x << " = " << (x) << endl #else #define debug(...) (void(0)) #define dump(x) (void(0)) #endif template void scan(vector& v, T offset = T(0)) { for (auto& x : v) { cin >> x; x += offset; } } // suc : 1 = newline, 2 = space template void print(T x, int suc = 1) { cout << x; if (suc == 1) cout << "\n"; else if (suc == 2) cout << " "; } template void print(const vector& v, int suc = 1) { for (int i = 0; i < v.size(); ++i) print(v[i], i == int(v.size()) - 1 ? suc : 2); } template void show(T x) { print(x, 1); } template void show(Head H, Tail... T) { print(H, 2); show(T...); } struct prepare_io { prepare_io() { cin.tie(nullptr); ios::sync_with_stdio(false); cout << fixed << setprecision(10); } } prep_io; #pragma endregion satashun const double pi = acos(-1.0); const double INF = 1e19; void slv() { int N, X; cin >> N >> X; V H(N + 1); for (int i = 1; i <= N; ++i) cin >> H[i]; V A(N); cin >> A; double ans = X * A[0]; // on the border auto calc = [&](double th) -> double { double ds = 0; double tm = 0; double res = INF; rep(j, N) { double wi = H[j + 1] - H[j]; double nd = ds + wi * tan(th); if (nd > X / 2) { tm = tm * 2 + (X - ds * 2) * A[j]; chmin(ans, tm); chmin(res, tm); return res; } chmin(res, tm * 2 + (X - ds * 2) * A[j]); nd = ds; ds += wi * tan(th); tm += wi / cos(th) * A[j]; th = asin(sin(th) * A[j] / A[j + 1]); } chmin(ans, res); return res; }; double lo = 0, hi = pi / 2; rep(t, 1000) { double u1 = (lo * 2 + hi) / 3; double u2 = (lo + hi * 2) / 3; if (calc(u1) < calc(u2)) { hi = u2; } else { lo = u1; } } show(ans); } int main() { int cases = 1; cin >> cases; rep(i, cases) slv(); return 0; }