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>
#include <vector>
using namespace std;

int main() {
	int n;
	double ax,ay,bx,by,cx,cy,dx,dy;
	vector<int> r;
	cin >> n;
	for (int i=0; i<n; i++)
	{
		cin >> ax >> ay >> bx >> by >> cx >> cy >> dx >> dy;
		if (ax == bx)
		{
			cx == dx ? r.push_back(1) : r.push_back(0);
		} else if (cx == dx) {
			r.push_back(0);
		} else {
			(ay-by)/(ax-bx) == (cy-dy)/(cx-dx) ? r.push_back(1) : r.push_back(0);
		}
	}
	for (int i=0; i<n; i++)
	{
		r[i] == 1 ? cout << "YES" << endl : cout << "NO" << endl;
	}
	return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
const double eps = 1e-7;

int main() {
    int n;
    double x1, y1, x2, y2, x3, y3, x4, y4;
    cin >> n;
    while(n--) {
        cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
        cout << (fabs((x2-x1)*(y4-y3) - (x4-x3)*(y2-y1)) < eps ? "YES" : "NO") << endl;
    }
    return 0;
}

C++: #include<bits/stdc++.h>
#define REP(i,n) for(int i=0;i<n;i++)
#define LOOP(i,x,n) for(int i=x;i<n;i++)
#define ALL(v) (v).begin(),(v).end()
#define PB push_back
#define MP make_pair
#define FR first
#define SC second
#define int long long
const double eps=1e-9;
using namespace std;
const int MOD=1000000007;
const int INF=9000000009;

signed main(){
  int n;
  cin>>n;
  while(n--){
    double x1,y1,x2,y2,x3,y3,x4,y4;
    cin>>x1>>y2>>x2>>y2>>x3>>y3>>x4>>y4;
    double a=(y2-y1)/(x2-x1),b=(y4-y3)/(x4-x3);
    cout<<(abs(a-b)<eps?"YES":"NO")<<endl;
  }
  return 0;
}

C++: #include<iostream>
#include<cmath>
using namespace std;
int main(){
  int n; cin >> n;
  while(n--){
    double x[4],y[4];
    for(int i=0;i<4;i++) cin >> x[i] >> y[i]; 
    if(abs((x[3] - x[2]) * (y[1] - y[0]) - (x[1] - x[0]) * (y[3] - y[2])) < 1e-5)
      cout<<"YES"<<endl;
    else
      cout<<"NO"<<endl;
  }
}

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

int main()
{
	int n;
	setprecision(5);
	double x[4], y[4],d1,d2,d3,d4;
	int ans[100];
	cin >> n;
	for (int a = 0; a < n; a++) {
		cin >> x[0] >> y[0] >> x[1] >> y[1] >> x[2] >> y[2] >> x[3] >> y[3];
		if (x[0] > x[1]) {
			d1 = x[0] - x[1];
			d3 = y[0] - y[1];
		}
		else {
			d1 = x[1] - x[0];
			d3 = y[1] - y[0];
		}
		if (x[2] > x[3]) {
			d2 = x[2] - x[3];
			d4 = y[2] - y[3];
		}
		else {
			d2 = x[3] - x[2];
			d4 = y[3] - y[2];
		}

		if (d3 / d1 == d4 / d2)
			ans[a] = 0;
		else
			ans[a] = 1;
	}
	for (int b = 0; b < n; b++) {
		if (ans[b] == 0)
			cout << "YES" << endl;
		else if (ans[b] == 1)
			cout << "NO" << endl;
	}
}

C++: #include <iostream>
#include <cstdio>
#include <cmath>
#include <cstdlib>
using namespace std;
int main(){
	int n;
	double x1,y1,x2,y2,x3,y3,x4,y4;
	cin>>n;
	for(int i=0;i<n;i++){
		cin>>x1>>y1>>x2>>y2>>x3>>y3>>x4>>y4;
		double a,b,c,d,e,f;
		a=sqrt(pow(x2-x1,2)+pow(y2-y1,2));
		c=sqrt(pow(x4-x3,2)+pow(y4-y3,2));
		b=abs(x1-x3);
		d=abs(x2-x4);
		e=abs(y1-y3);
		f=abs(y2-y4);
		if(a==c&&b==d&&e==f){
			cout<<"YES"<<endl;
		}else{
			cout<<"NO"<<endl;
		}
	}
	return 0;
}

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

int main()
{
    int n;
    cin >> n;
    for(int i=0; i<n; i++)
    {
        double x1, x2, x3, x4;
        double y1, y2, y3, y4;
        cin >>  x1 >>  y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
        if(abs((x4 - x3) * (y2 - y1) - (x2 - x1) * (y4 - y3)) <= 0.000000001)
        {
           cout << "YES" << endl; 
        }
        else
        {
            cout << "NO" << endl; 
        }
    }
    return 0;
}

C++: #include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <cmath>
#include <cstdio>
#include <functional>
#include <numeric>
#include <stack>
#include <queue>
#include <map>
#include <set>
#include <utility>
#include <sstream>
#include <complex>

using namespace std;

#define FOR(i,a,b) for(long long i=(a);i<(b);i++)
#define REP(i,N) for(long long i=0;i<(N);i++)
#define ALL(s) (s).begin(),(s).end()
#define fi first
#define se second

#define PI acos(-1.0)
#define INF 1000000007

typedef long long ll;
typedef pair<ll, ll> P;
typedef pair<double, double> PD;
typedef pair<string, ll> PS;
typedef vector<ll> V;

int n;
double X1, X2, X3, X4, Y1, Y2, Y3, Y4;

int main(){
	cin >> n;
	REP(i, n){
		cin >> X1 >> Y1 >> X2 >> Y2 >> X3 >> Y3 >> X4 >> Y4;
		if ((X2 - X1)*(Y4 - Y3) == (X4 - X3)*(Y2 - Y1)){
			cout << "YES" << endl;
		}
		else{
			cout << "NO" << endl;
		}
	}
}

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

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

using namespace std;

typedef complex<double> xy_t;
double dot_product(xy_t a, xy_t b){ return (conj(a) * b).real(); }
double cross_product(xy_t a, xy_t b){ return (conj(a) * b).imag(); }

int main(){
    int n;
    xy_t p[4];
    double x,y;
    cin >> n;
    REP(i,n){
        REP(j,4){
            cin >> x >> y;
            p[j] = xy_t (x,y);
        }
        if(!cross_product(p[0] - p[1], p[2] - p[3])) cout << "YES" << endl;
        else cout << "NO" << endl;
    }
}

C++: #include<iostream>

int main(){

	int n;
	std::cin >> n;

	for (int i = 0; i < n; i++){

		float x1, y1, x2, y2, x3, y3, x4, y4;
		std::cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;

		if (((y2 - y1) / (x2 - x1)) == ((y4 - y3) / (x4 - x3)))std::cout << "YES" << std::endl;
		else std::cout << "NO" << std::endl;
	}

	return 0;
}

C++: #define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <cstdio>
#include <cstring>
#include <ctime>
#include <string>
#include <vector>
#include <algorithm>
#include <cmath>
#include <sstream>
#include <utility>
using namespace std;
//typedef long long ll;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef pair<int,int> pii;
#define all(c) (c).begin(), (c).end()
#define loop(i,a,b) for(ll i=a; i<ll(b); i++)
#define rep(i,b) loop(i,0,b)
#define each(e,c) for(auto&e:c)
#define pb push_back
#define eb emplace_back
#define mp make_pair
#define mt make_tuple
#define lb lower_bound
#define ub upper_bound
#ifdef DEBUG
#define dump(...) (cerr<<#__VA_ARGS__<<" = "<<(DUMP(),__VA_ARGS__).str()<<" ["<<__LINE__<<"]"<<endl)
struct DUMP:ostringstream{template<class T>DUMP &operator,(const T&t){if(this->tellp())*this<<", ";*this<<t;return *this;}};
#else
#define dump(...)
#endif
 
int main(){
    int n; cin>>n;
    rep(_,n){
        double x[2][2], y[2][2];
        rep(i,2){
            rep(j,2){
                double x_,y_;
                cin >> x_ >> y_;
                x[i][j] = x_;
                y[i][j] = y_;
            }
        }
        double dx1=x[0][0]-x[0][1], dy1=y[0][0]-y[0][1];
        double dx2=x[1][0]-x[1][1], dy2=y[1][0]-y[1][1];
        //dump(dx1,dx2,dy1,dy2);
        puts(dx1*dy2==dx2*dy1 ? "YES" : "NO");
    }
}