// Author: Sahil Yasar

// #include <bits/stdc++.h>
#include <iostream>
#include <cmath>
#include <iomanip>
using namespace std;
#define endl '\n'

// #include <ext/pb_ds/assoc_container.hpp>
// #include <ext/pb_ds/tree_policy.hpp>
// using namespace __gnu_pbds;
// template<class T>
// using oset = tree<T, null_type, less<T>, rb_tree_tag,
//              tree_order_statistics_node_update>;
// template <class K, class V> using ht = gp_hash_table<K, V>;

template <class T1, class T2> ostream& operator<<(ostream& out, const pair<T1, T2> p)
{ return out<<'('<<p.first<<", "<<p.second<<")"; }
template <class ...Args> auto &print(const Args &...args)
{ return ((cerr<<args<<", "), ...)<<"\b\b)"<<endl; }
#define watch(...) if(true){cerr<<"("#__VA_ARGS__") = ("; print(__VA_ARGS__);}

#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define sz(x) (int)x.size()
#define f first
#define s second
#define read(arr) for(auto& x: arr) cin>>x
#define write(arr) for(auto& x: arr) cout<<x<<" "; cout<<endl
#define mem(x, n) memset(x, n, sizeof(x))
#define getUnique(x) sort(all(x)); x.erase(unique(all(x)), x.end());

typedef long long ll;
typedef long double ld;
typedef unsigned long long ull;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;

const double PI = acos(-1);

int main(){
    cin.tie(0)->sync_with_stdio(0);
    cin.exceptions(cin.failbit);

    int t, nt, at, nb, ab;
    double theta, alpha, beta, ans, rt, rb, x, p, c, a, len;
    cout<<fixed<<setprecision(6);
    cin>>t;
    while(t--){
        cin>>nt>>at>>nb>>ab;

        theta = 2 * PI / nb;
        alpha = (PI - theta)/2;
        x = sin(alpha)/sin(theta) * ab;
        rb = sqrt(x*x - ab*ab/4.0); // Radius of of inscribed circle of bottom polygon
        p = nb/2.0 * x*x * sin(theta); // Area of bottom polygon

        theta = 2 * PI / nt;
        alpha = (PI - theta)/2;
        x = sin(alpha)/sin(theta) * at;
        rt = sqrt(x*x - at*at/4.0); // Radius of of inscribed circle of top polygon
        c = PI*rt*rt; // Area of inscribed circle of top polygon

        a = len = 0;
        if (rt > rb){
            len = 2*sqrt(rt*rt - rb*rb);
            if (len <= ab){
                beta = 2*acos(rb/rt);
                a = beta/2*rt*rt - rb*len/2; // For inclusion exclusion
            }
        }

        ans = (len > ab)? 0: p-c+nb*a;
        cout<<ans<<endl;
    }

    return 0;
}