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[1] == fpoints[3] {
			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 <iostream>
#include <sstream>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <ctime>
#include <cstring>
#include <climits>
#include <algorithm>
#include <map>
#include <set>
#include <stack>
#include <vector>
#include <queue>
#include <string>
#include <complex>
using namespace std;

#define rep(i,n) for(int i=0; i<n; i++)
#define repa(i,s,e) for(int i=s; i<=e; i++)
#define repd(i,s,e) for(int i=s; i>=e; i--)

typedef long long ll;
typedef vector<int> vi;

// geometry library start

const double EPS = 1.0e-10;

class P {
public:
	double x, y;
	P() {}
	P(int x_, int y_) : x(x_), y(y_) {}
	P(double x_, double y_) : x(x_), y(y_) {}
	P(const P& p) : x(p.x), y(p.y) {}
	P operator+(const P& p) const { return P(x+p.x, y+p.y); } 
	P operator-(const P& p) const { return P(x-p.x, y-p.y); }
	P operator-() const { return P(-x, -y); }
	P operator*(double s) const { return P(x*s, y*s); }
	P operator/(double s) const { return P(x/s, y/s); }
	P& operator=(const P& p) { x=p.x; y=p.y; return (*this); }
	double dot(const P& p) const { return x*p.x + y*p.y; }
	double det(const P& p) const { return x*p.y - y*p.x; }
	double norm() const { return sqrt(x*x + y*y); }
	double norm2() const { return x*x + y*y; }
	P proj(const P& p) const { double k=det(p)/norm2(); return P(x*k, y*k); }
};

double tri(P a, P b, P c) { return (b - a).det(c - a); }
int sign(double r) { return r < -EPS ? -1 : r > EPS ? 1 : 0; }

class L {
public:
	P s, t;
	L() {}
	L(P s_, P t_) : s(s_), t(t_) {}
	L(const L& l) : s(l.s), t(l.t) {}
	L& operator=(const L& l) { s=l.s; t=l.t; return (*this); }
	double length() { return (s - t).norm(); }
	P vec() const { return t - s; }
	P proj(const P& p) { return s + vec().proj(p - s); }
	int iLL(const L& l) const {
		if(sign(vec().det(l.vec()))) return 1;
		if(sign(vec().det(l.s - s))) return 0;
		return -1;
	}
	bool iLS(const L& l) const { return sign(tri(s, t, l.s)) * sign(tri(s, t, l.t)) <= 0; } 
	bool iSS(const L& l) const { return iLS(l) && l.iLS(*this); }
	P pLL(const L& l) const { return s + vec() * (l.s - s).det(l.vec()) / vec().det(l.vec()); }
	double dLP(const P& p) const { return abs(tri(s, t, p)) / vec().norm(); }
	double dSP(const P& p) const {
		if(sign(vec().dot(p - s)) <= 0) return (p - s).norm();
		if(sign(vec().dot(p - t)) >= 0) return (p - t).norm();
		return dLP(p);
	}
};

class C {
public:
	P p;
	double r;
	C() {}
	C(P p_, double r_) : p(p_), r(r_) {}
	C(const C& c) : p(c.p), r(c.r) {}
	C& operator=(const C& c) { p=c.p; r=c.r; return (*this); }
};

// geometry library end

int main() {
	int n;
	double x1,y1,x2,y2,x3,y3,x4,y4;
	scanf("%d", &n);
	rep(i,n) {
		scanf("%lf%lf%lf%lf%lf%lf%lf%lf",&x1,&y1,&x2,&y2,&x3,&y3,&x4,&y4);
		P p1(x1,y1);
		P p2(x2,y2);
		P p3(x3,y3);
		P p4(x4,y4);
		if(sign((p2-p1).det(p4-p3)) == 0) {
			printf("YES\n");
		} else {
			printf("NO\n");
		}
	}
}

C++: #include <vector>
#include <map>
#include <set>
#include <stack>
#include <queue>
#include <algorithm>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <string>
#include <cstring>
#include <complex>
#include <ctime>
#include <cstdlib>
 
using namespace std;
 
inline int to_int(string s) {int v; istringstream sin(s); sin >> v; return v;}
template<class T> inline string to_str(T x) {ostringstream sout; sout << x; return sout.str();}
 
typedef long long ll;
 
int main()
{
    int num;
    double sx1, sy1, sx2, sy2;
    double ex1, ey1, ex2, ey2;
 
    cin >> num;
 
    for(int i = 0; i < num; i++)
    {
        cin >> sx1 >> sy1 >> sx2 >> sy2 >> ex1 >> ey1 >> ex2 >> ey2;
 
        if( (sy2-sy1)/(sx2 - sx1) == (ey2-ey1)/(ex2-ex1))
        {
            cout << "YES" << endl;
        }
        else
        {
            cout << "NO" << endl;
        }
    }
}

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 EPS = 0.000000001;
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;
    if (x1 - x2 < EPS && x3 - x4 < EPS) {
      cout << "YES" << endl;
      continue;
    }
    if (x1 - x2 < EPS || x3 - x4 < EPS) {
      cout << "NO" << endl;
      continue;
    }
    if ((y1 - y2) * (x3 - x4) - (y3 - y4) * (x1 - x2) < EPS) {
      cout << "YES" << endl;
    } else {
      cout << "NO" << endl;
    }
  }
}

C++: #include <iostream>
using namespace std;
int main(){
  int n;
   float 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;
    if( (y2-y1)/(x2-x1) == (y4-y3)/(x4-x3) ) 
      cout<<"YES\n";
    else
      cout<<"NO\n";
  }
  
  return 0;
}

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

struct point {
    double x;
    double y;
};

bool isparallel(point p1, point p2)
{
    if(p1.x ==0 && p1.y==0) return false;
    if(p2.x ==0 && p2.y==0) return false;
    if(((p1.x * p2.y) - (p1.y * p2.x)) ==0) return true;
    else return false;
}

int main()
{
    int n;
    double x1, y1, x2, y2, x3, y3, x4, y4;
    point p1, p2;
    cin >> n;
    for(int c=0; c< n; c++)
    {
        cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
        p1.x = x2 - x1;
        p2.x = x4 - x3;
        p1.y = y2 - y1;
        p2.y = y4 - y3;
        if(isparallel(p1, p2)) cout << "YES" << endl;
        else cout << "NO" << endl;
    }
    return EXIT_SUCCESS;
}