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 <cstdio>
using namespace std;
int main(){
	int n;
	cin >> n;
	for(int i=0;i<n;i++){
		double x1,x2,x3,x4,y1,y2,y3,y4;
		cin>>x1>>y1>>x2>>y2>>x3>>y3>>x4>>y4;
		double v1x = x2-x1;
		double v1y = y2-y1;
		double v2x = x4-x3;
		double v2y = y4-y3;
		double op = v1x*v2y-v1y*v2x;
		if(op<0.000001) cout << "YES" << endl;
		else cout << "NO" << endl;
	}
}

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

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

  for(int i=0;i<n;i++){
    complex<double> v[4];
    for(int j=0;j<4;j++){
      double x,y;
      cin >> x >> y;
      v[j]=complex<double>(x,y);
    }

    if(arg(v[1]-v[0])==arg(v[3]-v[2]))
      cout << "YES" << endl;
    else
      cout << "NO" << endl;
  }

  return 0;
}

C++: #include<iostream>
using namespace std;
int main()
{
	double x1,y1,x2,y2,x3,y3,x4,y4;
	int n;
	cin>>n;
	int N[100];
for(int i=0;i<n;i++)
{
	cin>>x1>>y1>>x2>>y2>>x3>>y3>>x4>>y4;
	if((y1-y2)/(x1-x2)==(y3-y4)/(x3-x4))
	{
	cout<<"YES"<<endl;
	}
	else
	{
	cout<<"NO"<<endl;
	}
}
return 0;
}

C++: #include <cmath>
#include <iostream>
#include <string>
#include <cstdlib>
#include <cstdio>
#include <algorithm>
#include <sstream>

using namespace std;

typedef struct{
    double x;
    double y;
}vec;

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

C++: 
#include <iostream>
#include <stdio.h>
#include <fstream>
#include <algorithm>
#include <string>
#include <list>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <vector>
#include <limits.h>
#include <math.h>
#define rep(i,n) for (int i = 0; (i) < (n); ++ (i))
using namespace std;

int main(void){
    int n;
    double x[4],y[4],a,b,c,d,det;
    cin >> n;
    rep(j,n) {

    
    //入力を多少簡略化
    for(int i=0;i<4;i++) {
        cin >> x[i];
        cin >> y[i];
    }
    //(x1,y1)(x2,y2)を結ぶax+by=p の係数
    a = y[0]-y[1];  b = x[1]-x[0];
    //(x3,y3)(x4,y4)を結ぶcx+dy=q の係数
    c = y[2]-y[3];  d = x[3]-x[2];
    //係数についての行列式
    det = a*d-c*b;
    if(det == 0) cout << "YES" << endl;
    else cout << "NO" << endl;
    }
}

C++: #include <bits/stdc++.h>

using namespace std;

typedef complex<double> P;

double const EPS = 1e-10;

double cross(P const& a, P const& b) {
  return imag(conj(a)*b);
}

bool is_parallel(P const& a1, P const& a2, P const& b1, P const& b2)
{ return abs(cross(a2-a1, b2-b1)) <= EPS; }

int main() {
  
  int N; cin >> N;
  for(int i=0; i<N; i++) {
    P ps[4];
    for(int i=0; i<4; i++)
      cin >> ps[i].real() >> ps[i].imag();
    printf("%s\n", (is_parallel(ps[0], ps[1], ps[2], ps[3]) ? "YES" : "NO" ));
  }
  
  return 0;
}

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

bool hantei(double x[], double y[]);

int main() {
  int n;
  double x[4], y[4];
  scanf("%d", &n);
  for(int i=0;i<n;i++) {
    for(int j=0;j<4;j++) scanf("%lf %lf", &x[j], &y[j]);
    if(hantei(x, y))
      printf("YES\n");
    else printf("NO\n");
  }
}

bool hantei(double x[], double y[]) {
  if(x[1]-x[0]/y[1]-y[0] == x[3]-x[2]/y[3]-y[2]) return true;
  //if(x[0]-x[3] == x[1]-x[2] && y[0]-y[3] == y[1]-y[2]) return true;
  return false;
}

C++: #include <iostream>
using namespace std;
int main(){
	int n;
	cin >> n;
	while(n--){
		double x1, y1, x2, y2, x3, y3, x4, y4, o;
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
		o = (x2-x1)*(y4-y3) - (y2-y1)*(x4-x3);
		if(!o) cout << "YES" << endl;
		else cout << "NO" << endl;
	}
	return 0;
}

C++: #include <iostream>
 
int main(){
     
    long double x1,y1,x2,y2,x3,y3,x4,y4;
int a;
    std::cin>>a;
    for(int s=0;s<a;s++){
        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++: //二次元幾何ライブラリ
#include <iostream>
#include <cstdio>
#include <complex>
#include <map>
#include <vector>

using namespace std;

#define rep(i, n) for (int i = 0; i < int(n); ++i)
#define MC make_pair
#define ML make_pair 
#define X real()
#define Y imag()
typedef double D;
typedef bool B;
typedef complex<D> P;   //点
typedef complex<D> V;   //ベクトル
typedef pair<P,P>  L;   //直線
typedef pair<P,D>  C;   //円
typedef vector<P>  Pol; //多角形

//変数名定義
const D INF = 1e100;
const D EPS = 1e-8;
const D PI = acos(-1);

template<class T> bool operator==(T a, T b){return abs(a - b )< EPS;}
template<class T> int sig(T r) {return (r==0||r==-0) ? 0 : r > 0 ? 1 : -1;}

P p3,p4;
int num;

// ベクトルaの絶対値を求める
// D Length = abs(a);

// 2点a,b間の距離を求める
// D Distance = abs(a-b); 

// 内積 (Inner Product) : a・b = |a||b|cosθ 1
D IP(V a, V b) {
	return (a.real() * b.real() + a.imag() * b.imag());
}

// 外積 (Exterior Product) : |a×b| = |a||b|sinθ 2
D EP(V a, V b) {
	return (a.real() * b.imag() - a.imag() * b.real());
}

// 点の進行方向について 3
int ccw(P a, P b, P c) {              //点aと点bが与えられた問いに
  b -= a; c -= a;
  if (EP(b, c) > 0)   return +1;      // counter clockwise
  if (EP(b, c) < 0)   return -1;      // clockwise
  if (IP(b, c) < 0)     return +2;    // c--a--b on line
  if (norm(b) < norm(c)) return -2;   // a--b--c on line
  return 0;                           // a--c--b on line  aとbの線分判定はこれ
}

// 2直線の垂直判定 : a⊥b <=> IP(a, b) = 0 4needs1
B IsVecular(L l1, L l2) {
	return IP(l1.first-l1.second, l2.first-l2.second)==0.0;
}

// 2直線の平行判定 : a//b <=> EP(a, b) = 0 5needs2
B IsParallel(L l1, L l2) {
	return EP(l1.first-l1.second, l2.first-l2.second)== 0.0;
}


//example : v1 = V(5.0,-3.0) p1=P(0.0,4.0)
int main(void){
	int n;
	cin >> n;
	for(int i=0;i<n;i++){
		P points[4];
		for(int j=0;j<4;j++)
			cin >> points[j].X >> points[j].Y;
		L l1,l2;
		l1=ML(points[0],points[1]);
		l2=ML(points[2],points[3]);
		if(IsParallel(l1,l2))
			cout << "YES" << endl;
		else
			cout << "NO" << endl;
	}
	return 0;
}