Go: package main

import "fmt"

func abs(x float64) float64 {
	if x < 0 {
		return -x
	}
	return x
}

func main() {
	var n int
	var x1, y1, x2, y2, x3, y3, x4, y4 float64
	fmt.Scan(&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)
		if abs((x2-x1)*(y4-y3) - (y2-y1)*(x4-x3)) < 1e-10 {
			fmt.Println("YES")
		} else {
			fmt.Println("NO")
		}
	}
}

C++: #include<iostream>
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;
    long long int xx1,yy1,xx2,yy2,xx3,yy3,xx4,yy4;
    xx1 = x1*100000;
    yy1 = y1*100000;
    xx2 = x2*100000;
    yy2 = y2*100000;
    xx3 = x3*100000;
    yy3 = y3*100000;
    xx4 = x4*100000;
    yy4 = y4*100000;

    long long int abx=x1-x2;
    long long int aby=y1-y2;
    long long int cdx=x3-x4;
    long long int cdy=y3-y4;
    if(abx == 0 && cdx == 0){
      cout<<"YES"<<endl;
    }
    else if(abx == 0 || cdx == 0){
      cout<<"NO"<<endl;
    }else if(aby*cdx == cdy*abx)
      cout<<"YES"<<endl;
    else
      cout<<"NO"<<endl;
  }
  return 0;
}

C++: #include <cstdio>

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

C++: #include<iostream>
#include<string>
#include<vector>
#include<cstdio>
#include<sstream>
#include<algorithm>
#include<cmath>
#include<map>
#include<functional>
#include<queue>
#include<stack>
#include<set>
using namespace std;
#define SZ(n)  (int)n.size()
#define dump(x) cerr<<#x<<" = "<<(x)<<endl;
#define debug(x)cerr << #x << " = " << (x) << " (L" << __LINE__ << ")" << " " << __FILE__ << endl;
#define MP make_pair
#define PB push_back
	double EPS=1e-10;
	bool same(double a,double b){
		if(fabs(a-b)<=EPS)return 1;
		else return 0;
	}
	
	
	int main(){
	int n;
	cin>>n;
	for(int i=0;i<n;i++){
		double x1,y1,x2,y2,x3,y3,x4,y4;
		cin>>x1>>y1>>x2>>y2>>x3>>y3>>x4>>y4;
		double a1=(y2-y1)/(x2-x1);
		double a2=(y4-y3)/(x4-x3);
		if(same(a1,a2))cout<<"YES"<<endl;
		else cout<<"NO"<<endl;
	}
	
	return 0;
}

C++: #include <cassert>
#include <cmath>
#include <iostream>
#include <vector>
#include <iomanip>

struct Point
{
    double x;
    double y;
};
struct Line
{
    Line(const Point& a, const Point& b)
    : p1(a), p2(b) {}
    Point p1;
    Point p2;
};
double GetSlope(const Line& line)
{
    return
    (line.p2.y - line.p1.y) /
    (line.p2.x - line.p1.x);
}
bool IsParallel(const Line& l1, const Line&l2)
{
    // std::cerr << std::fixed << std::setprecision(100) << GetSlope(l1) << std::endl;
    // std::cerr << std::fixed << std::setprecision(100) << GetSlope(l2) << std::endl;
    return GetSlope(l1) == GetSlope(l2);
    // const double gosa = 1e-10;
    // double Slope1 = GetSlope(l1);
    // double Slope2 = GetSlope(l2);
    // return std::fabs(Slope1 - Slope2) < gosa;
}
bool IsParallel(const std::vector<Point>& points)
{
    assert(points.size() == 4);
    return IsParallel(Line(points[0], points[1]), Line(points[2], points[3]));
}
std::vector<Point> Input(std::istream& is)
{
    std::vector<Point> points(4);
    for(int i = 0; i < points.size(); ++i){
        is >> points[i].x >> points[i].y;
    }
    return points;
}
int main()
{
    int n;
    std::cin >> n;
    for(int i = 0; i < n; ++i) {
        std::vector<Point> points = Input(std::cin);
        // std::cout << (IsParallel(points) ? "YES" : "NO") << std::endl; 
        if(IsParallel(points)){
            std::cout << "YES";
        }else{
            std::cout << "NO";
        }
        std::cout << std::endl;
    }
    return 0;
}

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

int main(){
	int n;
	cin >> n;
	for(int i = 0; i < n; i++){
		float x[4], y[4];
		for(int j = 0; j < 4; j++){
			cin >> x[j] >> y[j];
		}
	//	float ab = 99999999, cd = 99999999;
	//	if(x[0] != x[1]) ab = (y[0]-y[1]) / (x[0]-x[1]);
	//	if(x[2] != x[3]) cd = (y[2]-y[3]) / (x[2]-x[3]);
	//	if(ab == cd) cout << "YES"<< endl;
	//	else cout << "NO" << endl;

		puts((y[1]-y[0])/(x[1]-x[0]) == (y[3]-y[2])/(x[3]-x[2])?"YES":"NO");
	}
	return 0;
}

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

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


    }
    return 0;
}

C++: #include<bits/stdc++.h>
using namespace std;
signed main(void){
	double x[4],y[4];
	int T;
	cin>>T;
	for(int t=1;t<=T;t++){
		for(int i=0;i<4;i++)
			cin>>x[i]>>y[i];
		if((y[1]-y[0])*(x[3]-x[2])==(x[1]-x[0])*(y[3]-y[2])) 
			cout<<"YES"<<endl;
		else
			cout<<"NO"<<endl;
	}
}

C++: //include
//------------------------------------------
#include <vector>
#include <list>
#include <map>
#include <set>
#include <deque>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <ctime>
#include <climits>
#include <queue>

using namespace std;

//typedef
//------------------------------------------
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef long long LL;

//container util
//------------------------------------------
#define ALL(a)  (a).begin(),(a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define PB push_back
#define MP make_pair
#define SZ(a) int((a).size())
#define EACH(i,c) for(typeof((c).begin()) i=(c).begin(); i!=(c).end(); ++i)
#define EXIST(s,e) ((s).find(e)!=(s).end())
#define SORT(c) sort((c).begin(),(c).end())

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

//constant
//--------------------------------------------
const double EPS = 1e-10;
const double PI  = acos(-1.0);

int main(){
  cin.tie(0);
  ios_base::sync_with_stdio(false);

  int N; cin >> N;
  REP(n,N){
	double x[4], y[4];
	REP(i,4)
	  cin >> x[i] >> y[i];
	x[0] -= x[1], y[0] -= y[1], x[2] -= x[3], y[2] -= y[3];
	double n1 = sqrt(x[0]*x[0]+y[0]*y[0]), n2 = sqrt(x[2]*x[2]+y[2]*y[2]);
	x[0] /= n1, y[0] /= n1, x[2] /= n2, y[2] /= n2;
	double dot = x[0]*x[2]+y[0]*y[2];
	if(abs(abs(dot)-1.) <= EPS)
	  cout << "YES" << endl;
	else
	  cout << "NO" << endl;
  }
  
  return 0;
}

C++: #include <iostream>
#include <stdio.h>
#include <string.h>
#include <string>
#include <algorithm>
#include <vector>
#define _USE_MATH_DEFINES
#include <math.h>
#define swap(a,b) {a=a+b; b=a-b; a=a-b;}
#define abs(a) (a > 0 ? a:-a)

using namespace std;


void q21() {
	int N;
	cin >> N;
	for (int i = 0; i < N; i++) {
		double ax, ay, bx, by, cx, cy, dx, dy;
		cin >> ax >> ay >> bx >> by >> cx >> cy >> dx >> dy;
		if (bx - ax == 0 || dx - cx == 0) {
			if (bx - ax == dx - cx) {
				cout << "YES" << endl;
				continue;
			}
		}
		else if (abs((by - ay) / (bx - ax) - (dy - cy) / (dx - cx)) <= 0.00000001 ){
			cout << "YES" << endl;
			continue;
		}
		cout << "NO" << endl;
	}
}

int main() {
	q21();
	return 0;
}