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)
		}
		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++: // 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) {
    double 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<bits/stdc++.h>
#define EPS (1e-10)
#define equals(a,b)(fabs((a)-(b))<EPS)
#define rep(i,n)for(int i=0;i<n;i++)
using namespace std;

struct Point {
	double x, y;
	Point(double x = 0, double y = 0) :x(x), y(y) {}
	Point operator*(double a) { return Point(a*x, a*y); }
	Point operator-(Point p) { return Point(x - p.x, y - p.y); }
};
struct Segment {
	Point p1, p2;
};
double cross(Point a, Point b) {
	return a.x*b.y - a.y*b.x;
}
bool isPrallel(Segment s1, Segment s2) {
	return equals(cross(s1.p2 - s1.p1, s2.p2 - s2.p1), 0.0);
}
int main() {
	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;
		Segment s1{ {x1,y1},{x2,y2} };
		Segment s2{ {x3,y3},{x4,y4} };
		puts(isPrallel(s1, s2) ? "YES" : "NO");
	}
}

C++: #include <iostream>
#include <stdio.h>
#include <string.h>
#include <string>
#include <algorithm>

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 ((by - ay) / (bx - ax) == (dy - cy) / (dx - cx)) {
			cout << "YES" << endl;
			continue;
		}
		cout << "NO" << endl;
	}
}

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

C++: #include <cmath>
#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(); }
const double eps = 1e-10;

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);
        }
        bool ans = fabs(cross_product(p[0] - p[1], p[2] - p[3])) < eps;
        cout << (ans ? "YES" : "NO") << endl;
    }
}

C++: #include <string>
#include <vector>
#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<stack>
#include<queue>
#include<cmath>
#include<algorithm>
#include<functional>
#include<list>
#include<deque>
#include<bitset>
#include<set>
#include<map>
#include<cstring>
#include<sstream>
#include<complex>
#include<iomanip>
#include<numeric>
#define X first
#define Y second
#define pb push_back
#define rep(X,Y) for (int (X) = 0;(X) < (Y);++(X))
#define rrep(X,Y) for (int (X) = (Y-1);(X) >=0;--(X))
#define repe(X,Y) for ((X) = 0;(X) < (Y);++(X))
#define peat(X,Y) for (;(X) < (Y);++(X))
#define all(X) (X).begin(),(X).end()
#define rall(X) (X).rbegin(),(X).rend()

using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
template<class T> ostream& operator<<(ostream &os, const vector<T> &t) {
os<<"{"; rep(i,t.size()) {os<<t[i]<<",";} os<<"}"<<endl; return os;}
template<class S, class T> ostream& operator<<(ostream &os, const pair<S,T> &t) { return os<<"("<<t.first<<","<<t.second<<")";}

int main(){
  ios_base::sync_with_stdio(false);
  cout<<fixed<<setprecision(0);
  int i,j,k,T;
  cin>>T;
  while(T--){
    double xx,yy;
    ll x[4],y[4];
    rep(i,4){
      cin>>xx>>yy;
      x[i]=xx*1e5;
      y[i]=yy*1e5;
    }
    rep(i,2){
      x[i*2+1]-=x[i*2];
      y[i*2+1]-=y[i*2];
    }
    cout<<(x[1]*y[3]==x[3]*y[1]?"YES":"NO")<<endl;
  }
  return 0;
}

C++: #include<iostream>
#include<cstdio>
using namespace std;
#define int long long
signed main(){
        int n;
        scanf("%lld",&n);
        for(int i=0;i<n;i++){
                double x1, y1, x2, y2, x3, y3, x4, y4;
                scanf("%lf %lf %lf %lf %lf %lf %lf %lf", &x1, &y1, &x2, &y2, &x3, &y3, &x4, &y4);
                double c1 = (y2-y1)/(x2-x1);
                double c2 = (y4-y3)/(x4-x3);
                if((x2-x1==0 && x4-x3==0) || c1==c2) printf("YES\n");
                else printf("NO\n");
        }
        return 0;
}

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

const double eps=1e-9;

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    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)*(y4-y3)==(x4-x3)*(y2-y1)) cout<<"YES\n";
        else cout<<"NO\n";
    }
    return 0;
}

C++: #include <iostream>
#include <cmath>
using namespace std;
int main(){
  int n;
  double x[4],y[4];

  while(n--){
    for(int i = 0 ; i < 4 ; i++ )cin >> x[i] >> y[i];
    y[1]-=y[0];
    x[1]-=x[0];
    y[3]-=y[2];
    x[3]-=x[2];
    if(fabs(y[1]*x[3] - y[3]*x[1]) < 10e-8)cout << "YES";
    else cout << "NO";
    cout << endl;
    }
  return 0;
}

C++: #include <iostream>

int main(){
	double x1 , y1 , x2 , y2 , x3 , y3 , x4 , y4;
	bool parallel;
	int n;
	std::cin >> n;
	for(int i=0 ; i<n ; ++i){
		std::cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
		if(x1==x2 && x3==x4) {
			parallel=true;
			goto result;
		}
		else if(x1==x2 || x3==x4) {
			parallel=false;
			goto result;
		}
		else if ((y2-y1)/(x2-x1)==(y4-y3)/(x4-x3)) {
			parallel=true;
		}
		else {
			parallel=false;
		}
		result:
		std::cout << ( parallel ? "YES" : "NO") << std::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-10)
      cout<<"YES"<<endl;
    else
      cout<<"NO"<<endl;
  }
}