Go: package main

import (
	"bufio"
	"os"
	"strconv"
	"fmt"
	"strings"
)

var scanner = bufio.NewScanner(os.Stdin)

func nextInt() int {
	scanner.Scan()
	i, e := strconv.Atoi(scanner.Text())
	if e != nil {
		panic(e)
	}
	return i
}

func main() {
	n := nextInt()
	for i := 0; i < n; i++ {
		scanner.Scan()
		points := strings.Split(scanner.Text(), " ")
		fpoints := make([]float64, 0)
		for _, v := range points {
			tmp, _ := strconv.ParseFloat(v, 64)
			fpoints = append(fpoints, tmp)
		}
		if fpoints[0] == fpoints[2] && fpoints[4] == fpoints[6] {
			fmt.Println("YES")
			continue
		}
		a := (fpoints[1]-fpoints[3])/(fpoints[0]-fpoints[2])
		b := (fpoints[5]-fpoints[7])/(fpoints[4]-fpoints[6])
		if a == b {
			fmt.Println("YES")
		} else {
			fmt.Println("NO")
		}
	}
}

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

typedef complex<double> P;

// ?¨±?????????????????
#define EPS (1e-10)
// 2??????????????????????????????????????????
#define EQ(a,b) (abs((a)-(b)) < EPS)

// ?????? (cross product) : a??b = |a||b|sin??
double cross(P a, P b) {
  return (a.real() * b.imag() - a.imag() * b.real());
}

// 2??´?????????????????? : a//b <=> cross(a, b) = 0
int is_parallel(P a1, P a2, P b1, P b2) {
  return EQ( cross(a1-a2, b1-b2), 0.0 );
}

int main(){
	int n;
	double x1,x2,x3,x4,y1,y2,y3,y4;

	cin >> n;
	for(int i=0 ; i<n ; i++){
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
		P a(x1,y1), b(x2,y2), c(x3,y3), d(x4,y4);
		if( is_parallel(a,b,c,d) ){
			cout << "YES" << endl;
		}else{
			cout << "NO" << endl;
		}
	}
}

C++: #include<stdio.h>

int main(){

int N;
double x1,x2,x3,x4,y1,y2,y3,y4;
double a1=0,a2=0;

scanf("%d",&N);
for(int i=0;i<N;i++)
{
scanf("%lf %lf %lf %lf %lf %lf %lf %lf",&x1,&y1,&x2,&y2,&x3,&y3,&x4,&y4);
a1=(x1-x2)/(y1-y2);a2=(x3-x4)/(y3-y4);
if(a1==a2)printf("YES\n");
else if(a1!=a2)printf("NO\n");
}
return 0;
}

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

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

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

C++:  
 #include<iostream>
 #include<stdio.h>
 #include<string>
 #include<math.h>
 #include<iomanip>
 #include<algorithm>
 #include<string.h>
 #include<cctype>
 #include<map>
 #include<set>
 #include<vector>
 #include<sstream>
 #include<stack>
 
 using namespace std;
 
 double abs(double x)
 {
   if(x<0) return -x;
   else return x;       
 }
  
 int main()
 {
   double x1,y1,x2,y2,x3,y3,x4,y4;
   int n;
   cin>>n;
   while(n--)
   {
     cin>>x1>>y1>>x2>>y2>>x3>>y3>>x4>>y4;
    
       double k1=(y2-y1)/(x2-x1);
       double k2=(y4-y3)/(x4-x3);
       if((y2-y1)/(x2-x1)==(y4-y3)/(x4-x3)) cout<<"YES"<<endl;
       else cout<<"NO"<<endl;     
           
   }
   //while(1);      
   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 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

void solve() {
  int n;
  cin >> n;
  rep(i, n) {
    float x1, y1, x2, y2, x3, y3, x4, y4;
    cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
    cout << ((y2 - y1) / (x2 - x1) == (y4 - y3) / (x4 - x3) ? "YES" : "NO") << endl;
  }
}

C++: #include <iostream>
#include <string>
#include <cctype>
#include <cmath>
#include <stdio.h>
#include <algorithm>
#include <vector>
#include <map> // pair
#include <set>
#include <string>

#define MAXSIZE 200000
#define PI 3.141592653589
using namespace std;

template<typename T>
T add(T a,T b){
  return a+b;
}

namespace A
{
  int f(void){
    return 1;
  }
}


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

  for(int i=0;i<n;i++){
    double x1,y1,x2,y2,x3,y3,x4,y4;
    std::cin >> x1>>y1>>x2>>y2>>x3>>y3>>x4>>y4;

    if(((x1-x2)*(y3-y4)-(x3-x4)*(y1-y2))<0.0001){
      std::cout << "YES" << '\n';
    }else{
      std::cout << "NO" << '\n';
    }
  }
}

C++: #include <stdio.h>
struct point{
    double x;
    double y;
};
double abs(double a){
    if(a<0)return -a;
    return a;
}
double triangle(point a,point b,point c){
    return abs(a.x*b.y+b.x*c.y+c.x*a.y-a.y*b.x-b.y*c.x-c.y*a.x);
}
int main(){
    point a[4];
    while(scanf("%lf%lf",&a[0].x,&a[0].y)!=EOF){
        for(int i=1;i<4;i++)scanf("%lf%lf",&a[i].x,&a[i].y);
        if(triangle(a[0],a[1],a[2])==triangle(a[0],a[1],a[3])&&triangle(a[0],a[2],a[3])==triangle(a[1],a[2],a[3])){
            printf("YES\n");
        }
        else printf("NO\n");
    }
}

C++: #include <stdio.h>
 
int main(void) {
    int max;
    int i;
    int j;
    double x[4];
    double y[4];
    scanf("%d",&max);
    for(i=0;i<max;i++) {
        for(j=0;j<4;j++)scanf("%lf %lf",&x[j],&y[j]);
        if(x[0]==x[1]) {
            if(x[2]==x[3])printf("YES\n");
            else printf("NO\n");
        } else if(x[2]==x[3])printf("NO\n");
        else {
            if((y[1]-y[0])/(x[1]-x[0])==(y[3]-y[2])/(x[3]-x[2]))
                printf("YES\n");
            else printf("NO\n");
        }
    }
    return 0;
}

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

int main()
{
	int n;
	cin >> n;
	for (int i = 0; i < n; i++)
	{
		long double a[4][2];
		for (int I = 0; I< 4; I++)
		{
			for (int k = 0; k < 2; k++)
			{
				cin >> a[I][k];
			}
		}
		long double x, y;
		x = (a[1][0] - a[0][0]);
		y = (a[3][0] - a[2][0]);
		x = (x) ? (a[1][1] - a[0][1]) / x : 0;
		y = (y) ? (a[3][1] - a[2][1]) / y : 0;
		if (x == y)cout << "YES" << endl;
		else cout << "NO" << endl;
	}

}
/*
		x = (a[1][1] - a[0][1]) / (a[1][0] - a[0][0]);
		y = (a[3][1] - a[2][1]) / (a[3][0] - a[2][0]);*/