#include <cstdio>#include <cstring>#include <cmath>#include <algorithm>const double eps = 1e-8;const double pi = acos(-1.);const double inf = 1e30;using namespace std;int dblcmp( double x ){if( fabs(x) < eps )return x;return x > 0 ? 1 : -1;}struct point{double x, y, mr, r, ang, D;} p[1000], C;double ddd( point& a, point& b ){double dx = a.x - b.x;double dy = a.y - b.y;return sqrt(dx*dx+dy*dy);}void adjust( double& x ){while( dblcmp(x-2*pi) >= 0 )x -= 2*pi;while( x < 0 )x += 2*pi;}struct seg{double x;int st;} s[10000];int cmp( seg a, seg b ){if( fabs(a.x-b.x) > eps )return a.x < b.x;return a.st > b.st;}double dis[300][300];bool sure[300];void makeMaxRadius(int n) { memset(sure, false, sizeof (sure)); for (int k = 0; k < n; k++) { for (int i = 0; i < n; i++) { if (sure[i] == false) { p[i].mr = inf; } } for (int i = 0; i < n; i++) { for (int j = i + 1; j < n; j++) { if (sure[i] && sure[j]) { continue; } else if (sure[i]) { p[j].mr = min(p[j].mr, dis[i][j] - p[i].mr); } else if (sure[j]) { p[i].mr = min(p[i].mr, dis[i][j] - p[j].mr); } else { p[i].mr = min(p[i].mr, 0.5 * dis[i][j]); p[j].mr = min(p[j].mr, 0.5 * dis[i][j]); } } if (sure[i] == false) { p[i].mr = min(p[i].mr, ddd(C, p[i])); } } double minNum = inf; int minInd = -1; for (int i = 0; i < n; i++) { if (sure[i] == false && p[i].mr < minNum) { minNum = p[i].mr; minInd = i; } } sure[minInd] = true; }}int main(){int T, n, i, j, k, e, ok;double ll, rr, mid, ang, t;int a, b;C.x = C.y = 0;scanf("%d", &T);while( T-- ){ll = rr = 0;scanf("%d", &n);for( i = 0; i < n; ++i ){scanf("%d %d", &a, &b);p[i].x = a;p[i].y = b;}for( i = 0; i < n; ++i )for( j = 0; j < n; ++j )dis[i][j] = ddd(p[i], p[j]);for( i = 0; i < n; ++i ){p[i].D = ddd(p[i], C);p[i].mr = -1;p[i].ang = atan2(p[i].y, p[i].x);}for( k = 0; k < n; ++k ){double he = 1e20;for( i = 0; i < n; ++i )if( p[i].mr < 0 ){if( he > p[i].D ){he = p[i].D;e = i;}for( j = 0; j < n; ++j )if( i != j ){t = dis[i][j];if( p[j].mr > 0 ){if( t - p[j].mr < he ){he = t-p[j].mr;e = i;}}else if( t*0.5 < he ){he = t*0.5;e = i;}}}p[e].mr = he;}for( i = 0; i < n; ++i )if( p[i].mr > rr )rr = p[i].mr;rr += 10;ok = 0;for( int ii = 100; ii > 0; --ii ){mid = (ll+rr)*0.5;for( i = 0; i < n; ++i ){if( p[i].mr < mid )p[i].r = p[i].mr;elsep[i].r = mid;}e = 0;for( i = 0; i < n; ++i ){t = asin(p[i].r/p[i].D);t = fabs(t);s[e].x = p[i].ang-t;adjust(s[e].x);s[e++].st = 1;s[e].x = p[i].ang+t;adjust(s[e].x);s[e++].st = -1;if( s[e-2].x > s[e-1].x ){s[e].x = 0;s[e++].st = 1;s[e].x = 2*pi;s[e++].st = -1;}}sort(s, s+e, cmp);t = ang = 0;k = 0;for( i = 0; i < e; ++i ){if( !k )t = s[i].x;k += s[i].st;if( !k )ang += s[i].x - t;}if( dblcmp(ang-2*pi) )ll = mid;else{ok = 1;rr = mid;}}if( !ok )printf("-1.0n");elseprintf("%.8lfn", mid);}return 0;}
