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<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=0.0000000001;
	bool same(double a,double b){
		if(abs(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(a1==a2)cout<<"YES"<<endl;
		else cout<<"NO"<<endl;
	}
	
	return 0;
}

C++: #define	_USE_MATH_DEFINES
#include <iostream>
#include <algorithm>
#include <functional>
#include <vector>
#include <cstdio>
#include <string>
#include <cmath>
#include <cfloat>
#include <map>
#include <queue>
#include <stack>
#include <list>
using namespace std;

int main(){

	int n;
	cin>>n;
	double x1,y1,x2,y2,x3,y3,x4,y4;
	while(n>0){
		
		double a=999999,b=999999;
	cin>>x1>>y1>>x2>>y2>>x3>>y3>>x4>>y4;

		if(x2!=x1){
			a=(y2-y1)/(x2-x1);
		}
		if(x3!=x4){
			b=(y4-y3)/(x4-x3);
		}
		
		if(a==b)
			cout<<"YES"<<endl;
		else
			cout<<"NO"<<endl;
		
		n--;
	}
	
	
}

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

C++: #define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <cstdio>
#include <cstring>
#include <ctime>
#include <string>
#include <vector>
#include <algorithm>
#include <cmath>
#include <sstream>
#include <utility>
using namespace std;
typedef long long ll;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef pair<int,int> pii;
#define all(c) (c).begin(), (c).end()
#define loop(i,a,b) for(ll i=a; i<ll(b); i++)
#define rep(i,b) loop(i,0,b)
#define each(e,c) for(auto&e:c)
#define pb push_back
#define eb emplace_back
#define mp make_pair
#define mt make_tuple
#define lb lower_bound
#define ub upper_bound
#ifdef DEBUG
#define dump(...) (cerr<<#__VA_ARGS__<<" = "<<(DUMP(),__VA_ARGS__).str()<<" ["<<__LINE__<<"]"<<endl)
struct DUMP:ostringstream{template<class T>DUMP &operator,(const T&t){if(this->tellp())*this<<", ";*this<<t;return *this;}};
#else
#define dump(...)
#endif
 
int main(){
    int n; cin>>n;
    rep(_,n){
        ll x[2][2], y[2][2];
        rep(i,2){
            rep(j,2){
                double x_,y_;
                cin >> x_ >> y_;
                x[i][j] = x_*100000 + 0.1;
                y[i][j] = y_*100000 + 0.1;
            }
        }
        ll dx1=x[0][0]-x[0][1], dy1=y[0][0]-y[0][1];
        ll dx2=x[1][0]-x[1][1], dy2=y[1][0]-y[1][1];
        dump(dx1,dx2,dy1,dy2);
        puts(dx1*dy2==dx2*dy1 ? "YES" : "NO");
    }
}

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

int main() {
	double x1, y1, x2, y2, x3, y3, x4, y4;
	int n;
	double veku1[2];
	double veku2[2];
	cin >> n;
	for (int i = 0; i < n; i++) {
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
		veku1[0] = x2 - x1;
		veku1[1] = y2 - y1;
		veku2[0] = x4 - x3;
		veku2[1] = y4 - y3;
		if (abs(veku1[0]*veku2[1]-veku1[1]*veku2[0]) <= 0.0000001) {
			/*veku1[0] = x3 - x1;
			veku1[1] = y3 - y1;
			veku2[0] = x4 - x1;
			veku2[1] = y4 - y1;
			if (abs(veku1[0]*veku2[1]-veku1[1]*veku2[0]) <= 0.0000001) {
				cout << "NO" << endl;
			} else {*/
				cout << "YES" << endl;
			//}
		} else {
			cout << "NO" << endl;
		}
	}
	return 0;
}

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

using namespace std;

int main(){
	double x1,y1,x2,y2,x3,y3,x4,y4;
	int n;
	cin >> 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);
		x2-=x1; y2-=y1;
		x4-=x3; y4-=y3;
		if(x2*y4-y2*x4==0) printf("YES\n");
		else printf("NO\n");
	}
	return 0;
}

C++: #include <vector>
#include <map>
#include <set>
#include <stack>
#include <queue>
#include <deque>
#include <algorithm>
#include <utility>
#include <functional>
#include <sstream>
#include <iostream>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <ctime>
#include <climits>
using namespace std;
inline int toInt(string s) { int v; istringstream sin(s); sin >> v; return v;}
template<class T> inline string toString(T x) { ostringstream sout; sout << x; return sout.str();}
typedef vector<int> vi;
typedef vector<vi>  vvi;
typedef vector<string> vs;
typedef pair<int, int> pii;
typedef long long ll;
#define ALL(a) (a).begin(),(a).end()
#define RALL(a) (a).rbegin(),(a).rend()
#define EACH(t,i,c) for(t::iretator i=(c).begin(); i!=(c).end(); ++i)
#define EXIST(s,e) ((s).find(e)!=(s).end())
#define FOR(i,a,b) for(int i=(a);i<=(b);++i)
#define REP(i,n) FOR(i,0,n-1)
const double EPS = 1e-10;
const double PI = acos(-1.0);

#include <complex>
typedef complex<double> P;

struct L {
	P a, b;
	L(const P &a, const P &b) : a(a), b(b) { }
};

struct C {
	P p; double r;
	C(const P p, double r) : p(p), r(r) { }
};

double dot(P a, P b) {
	return real(conj(a)*b);
}

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

bool LLcross(L l1, L l2) {
	return abs(cross(l1.b-l1.a, l2.b-l2.a)) > EPS/* || abs(cross(l1.b-l1.a, l2.b-l1.a)) < EPS*/;
}

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

	REP(i, n) {
		double x1, y1, x2, y2;
		cin >> x1 >> y1 >> x2 >> y2;
		L l1(P(x1, y1), P(x2, y2));

		
		cin >> x1 >> y1 >> x2 >> y2;
		L l2(P(x1, y1), P(x2, y2));

		cout << (LLcross(l1, l2) ? "NO" : "YES") << endl;
	}

	return 0;
}

C++: #include <iostream>

int main() {
    int n;
    std::cin >> n;
    double x1,y1,x2,y2,x3,y3,x4,y4;
    
    for(int i = 0;i < n;i++){
        std::cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
        double a = (y1-y2)/(x1-x2);
        double b = (y3-y4)/(x3-x4);
         std::cout <<  (a==b ? "YES":"NO") << '\n';
    }
}

C++: #include <iostream>

int main() {
    int n;
    std::cin >> n;
    double x1,y1,x2,y2,x3,y3,x4,y4;
    
    for(int i = 0;i < n;i++){
        std::cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
        double a = (y1-y2)/(x1-x2);
        double b = (y3-y4)/(x3-x4);
         std::cout <<  (a==b ? "YES":"NO") << '\n';
    }
}

C++: #include<iostream>
#include<cmath>
using namespace std;
int main(){
  int n;
  double x[4],y[4];
  
  cin >> n;
  
  while(n--){
    for(int i=0;i<4;i++){
      cin >> x[i] >> y[i];
    }
    
    double a,b;
    a = (y[0]-y[1])*(x[2]-x[3]);
    b = (y[2]-y[3])*(x[0]-x[1]);

    if(fabs(a-b) < 0.00001) cout << "YES" << endl;
    else cout << "NO" << endl;
  }
  
  return(0);
}