Go: package main

import (
        "fmt"
        "math/big"
)

func main() {
        var x1, x2, x3, x4, y1, y2, y3, y4 big.Float
        var n int
        fmt.Scanf("%d", &n)
        for i := 0; i < n; i++ {
                fmt.Scanf("%f %f %f %f %f %f %f %f",
                        &x1, &y1, &x2, &y2, &x3, &y3, &x4, &y4)
                var lx, ly, mx, my, mul1, mul2, sub, zz big.Float
                lx.Sub(&x2, &x1)
                ly.Sub(&y2, &y1)
                mx.Sub(&x4, &x3)
                my.Sub(&y4, &y3)
                mul1.Mul(&lx, &my)
                mul2.Mul(&ly, &mx)
                sub.Sub(&mul1, &mul2)
                zz.SetFloat64(0.0)

                if sub.Cmp(&zz) == 0 {
                        fmt.Println("YES")
                } else {
                        fmt.Println("NO")
                }
        }
}

C++: #include <iostream>

using namespace std;

int main()
{
	int n;
	double x[4], y[4];

	cin >> n;

	for(int i = 0; i < n; i++){
		cin >> x[0] >> y[0] >> x[1] >> y[1] >> x[2] >> y[2] >> x[3] >> y[3];

		if((x[1]-x[0] == 0 && x[3]-x[2] == 0) || (y[1]-y[0] == 0 && y[3]-y[2] == 0))
			cout << "YES" << endl;
		else if(((y[1]-y[0])/(x[1]-x[0])) == ((y[3]-y[2])/(x[3]-x[2])))
			cout << "YES" << endl;
		else 
			cout << "NO" << endl;
	}

	return 0;
}

C++: // clang-format off
#include <bits/stdc++.h>
#define int long long
#define main signed main()
// #define main int main()
#define loop(i, a, n) for (int i = (a); i < (n); i++)
#define rep(i, n) loop(i, 0, n)
#define all(v) (v).begin(), (v).end()
#define rall(v) (v).rbegin(), (v).rend()
#define prec(n) fixed << setprecision(n)
#define stlice(from, to) substr(from, (to) - (from) + 1)
#define pb push_back
#define mp make_pair
#define mt make_tuple
#define fi first
#define se second
using namespace std;
using pii = pair<int, int>;
using vi = vector<int>;
using vd = vector<double>;
using vc = vector<char>;
using vb = vector<bool>;
using vs = vector<string>;
using vpii = vector<pii>;
using vvi = vector<vi>;
using vvb = vector<vb>;
using vvpii = vector<vpii>;
template<typename A> using fn = function<A>;
constexpr int INF = sizeof(int) == sizeof(long long) ? 1000000000000000000LL : 1000000000;
constexpr int MOD = 1000000007;
constexpr double EPS = 0.000000001;
constexpr double PI = acos(-1);
template<typename A, typename B> bool cmin(A &a, const B &b) { return a > b ? (a = b, true) : false; }
template<typename A, typename B> bool cmax(A &a, const B &b) { return a < b ? (a = b, true) : false; }
constexpr bool odd(const int &n) { return n & 1; }
constexpr bool even(const int &n) { return !odd(n); }
template<typename V> constexpr typename V::value_type sum(const V &v) { return accumulate(all(v), 0); }
void solve();
main { solve(); return 0; }
// clang-format on

#define double long double

void solve() {
  int n;
  cin >> n;
  rep(i, n) {
    double x1, y1, x2, y2, x3, y3, x4, y4;
    cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
    if (abs(x1 - x2) < EPS && abs(x3 - x4) < EPS) {
      cout << "YES" << endl;
      continue;
    }
    if (abs(x1 - x2) < EPS || abs(x3 - x4) < EPS) {
      cout << "NO" << endl;
      continue;
    }
    if (abs((y1 - y2) * (x3 - x4) - (y3 - y4) * (x1 - x2)) < EPS) {
      cout << "YES" << endl;
    } else {
      cout << "NO" << endl;
    }
  }
}

C++: #include <iostream>
#include <cstdio>

using namespace std;

#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n) FOR(i,0,n)

int main() {
	int n;
	float x[4], y[4];
	bool flag;
	cin >> n;
	REP(i,n) {
		flag = true;
		REP(j,4)
			cin >> x[j] >> y[j];
		REP(j,2) {
			if (x[(j*2+1)%4] == x[(j*2)%4] && x[((j+1)*2+1)%4] != x[((j+1)*2)%4])
				flag = false;
			if (y[(j*2+1)%4] == y[(j*2)%4] && y[((j+1)*2+1)%4] != y[((j+1)*2)%4])
				flag = false;
		}
		if (flag && !(x[1] == x[0] && x[3] == x[2] || y[1] == y[0] && y[3] == y[2])) {
			if ((y[1]-y[0])/(x[1]-x[0]) != (y[3]-y[2])/(x[3]-x[2]))
				flag = false;
		}

		if (flag)
			printf("YES\n");
		else
			printf("NO\n");
	}
	return 0;
}

C++: #include <iostream>
#include <cmath>
#include <vector>
#include <string>
#include <algorithm>
#include <climits>
using namespace std;

int main(){
    double e = 0.00000000001;
    double x[5];
    double y[5];
    double s;
    double t;
    double u;
    double v;
    double m;
    int n;
    cin >> n;

    for(int i = 0;i < n;i++){
        cin >> x[0] >> y[0] >> x[1] >> y[1] >> x[2] >> y[2] >> x[3] >> y[3];

        s = x[1] - x[0];
        t = y[1] - y[0];
        u = x[3] - x[2];
        v = y[3] - y[2];

        if(s * v - t * u > 0){
            double m = s * v - t * u;
        }
        else{
            double m = t * u - s * v;
        }

        if(m < e){
            cout << "YES" << endl;
        }
        else{
            cout << "NO" << endl;
        }
    }
    return 0;
}

C++: #include<iostream>
#include<cstdio>

using namespace std;

int main(){
	int n;
	cin >> n;

	double x1, y1, x2, y2, x3, y3, x4, y4;

	for (int i = 0; i < n;i++){
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
		double a, b;
		a = (y2 - y1) / (x2 - x1);
		b = (y4 - y3) / (x4 - x3);
		(a == b) ? cout << "YES" << endl : cout << "NO" << endl;
	}

	return 0;
}

C++: #include<bits/stdc++.h>
using namespace std;
 
signed main(){
int a;
cin>>a;
double c[8];
for(int b=0;b<a;b++){
    for(int d=0;d<8;d++)cin>>c[d];
    if(c[0]==c[2]&&c[4]==c[6])printf("YES\n");
    else if((c[6]-c[4])/(c[7]-c[5])==(c[2]-c[0])/(c[3]-c[1]))printf("YES\n");
    else printf("NO\n");s
    }
}

C++: #include<stdio.h>
#include<string>
#include<stdlib.h>
#include<math.h>
#include<iostream>
#include<vector>
#include<algorithm>
#include<numeric>
#include<string.h>
#include<map>
#include<queue>

using namespace std;

typedef pair<int,int> pii;

#define rep(i,j) for(int i=0;i<(j);i++)
#define reps(i,j,k) for(int i=j;i<=k;i++)
#define in(i,j,k) ((i)>=(j)&&(i)<=(k))


int main(){
	int n;
	double x[4],y[4],t;
	scanf("%d",&n);
	rep(j,n){
		rep(i,4)scanf("%lf%lf",x+i,y+i);
		rep(i,2){
			x[i]=x[i*2]-x[i*2+1];
			y[i]=y[i*2]-y[i*2+1];
		}
		puts(x[0]*y[1]-y[0]*x[1]==0?"YES":"NO");
	}
	return 0;
}

C++: #include <iostream>
using namespace std;
int main(){
  
  double x1, y1, x2, y2, x3, y3, x4, y4;
  int dataSets;
  cin >> dataSets;
  for(int i=0;i<dataSets;i++){
    bool flag=false;
    cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
    if((y2-y1)*(x4-x3) - (x2-x1)*(y4-y3)){
      flag = true;
    }

    if(flag){
      cout << "YES" << endl;
    }else{
      cout << "NO" << endl;
    }
    
  }

}

C++: #include<iostream>
using namespace std;

int main(){
  int n;
  double x[4],y[4];
  cin>>n;
  for(int i=0;i<n;i++){
    for(int j=0;j<4;j++)
      cin>>x[j]>>y[j];
    if((y[3]-y[2])*(x[1]-x[0])==(y[1]-y[0])*(x[2]-x[3])) cout<<"YES"<<endl;
    else cout<<"NO"<<endl;
  }
  return 0;
}

C++: #include<iostream>
#include<complex>
#include<cmath>
using namespace std;
typedef complex<double> xy;

int main() {
	int n;
	xy a, b, c, d;
	double delta = 1e-11;
	cin >> n;
	for (int i = 0; i < n; i++) {
		cin >> a.real() >> a.imag();
		cin >> b.real() >> b.imag();
		cin >> c.real() >> c.imag();
		cin >> d.real() >> d.imag();

		xy s = a - b, t = c - d;
		if (abs((conj(s)*t).imag()) < delta) cout << "YES" << endl;
		else cout << "NO" << endl;
	}

	return 0;

}