Go: package main

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

var scanner = bufio.NewScanner(os.Stdin)

func main() {
	scanner.Scan()
	n, _ := strconv.Atoi(scanner.Text())
	for i := 0; i < n; i++ {
		scanner.Scan()
		input := strings.Split(scanner.Text(), " ")
		buf := make([]float64, len(input))
		for j := range buf {
			buf[j], _ = strconv.ParseFloat(input[j], 64)
		}
		p1 := complex(buf[0], buf[1])
		p2 := complex(buf[2], buf[3])
		p3 := complex(buf[4], buf[5])
		pk := complex(buf[6], buf[7])
		ps := complex(buf[8], buf[9])
		kin := isAtSameSide(p3, pk, []complex128{p1, p2}) &&
			isAtSameSide(p1, pk, []complex128{p2, p3}) &&
			isAtSameSide(p2, pk, []complex128{p3, p1})
		sin := isAtSameSide(p3, ps, []complex128{p1, p2}) &&
			isAtSameSide(p1, ps, []complex128{p2, p3}) &&
			isAtSameSide(p2, ps, []complex128{p3, p1})
		if (kin || sin) && !(kin && sin) {
			fmt.Println("OK")
		} else {
			fmt.Println("NG")
		}
	}
}

func isAtSameSide(a, b complex128, line []complex128) bool {
	sa := (real(line[1]) - real(line[0]))*(imag(a)-imag(line[0]))+
		(imag(line[1])-imag(line[0]))*(real(line[0])-real(a))
	sb := (real(line[1]) - real(line[0]))*(imag(b)-imag(line[0]))+
		(imag(line[1])-imag(line[0]))*(real(line[0])-real(b))
	return (sa > 0 && sb > 0) || (sa < 0 && sb < 0)
}

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

#define EPS (1e-10)
typedef complex<double> Po;

double cross(Po x,Po y){return x.real()*y.imag() - x.imag()*y.real();}

double area(Po a,Po b,Po c){
  return abs(cross(b-a,c-a)/2);
}

bool inter(Po a,Po b,Po c,Po x){
  if( area(a,b,x) + area(b,c,x) + area(c,a,x) > area(a,b,c) + EPS)return false;
  else return true;
}

int main(){
  int n;
  Po p1,p2,p3,pk,ps;

  cin >> n;

  for(int i=0;i<n;i++){
    cin >> p1.real() >> p1.imag();
    cin >> p2.real() >> p2.imag();
    cin >> p3.real() >> p3.imag();
    cin >> pk.real() >> pk.imag();
    cin >> ps.real() >> ps.imag();

    if(inter(p1,p2,p3,pk) != inter(p1,p2,p3,ps) )cout << "OK" << endl;
    else cout << "NG" << endl;
  }
  
}

C++: #include <stdio.h>
#include <iostream>
#include <vector>
#include <string>
#include <math.h>
#include <algorithm>
using namespace std;
#define INF 0x7FFFFFFF
const double EPS = 1e-10;


inline bool eq(double a, double b) { return fabs(b - a) < EPS;}

struct p_t{
  double x;
  double y;
  double norm() { return x * x + y * y; }
  double abs() { return sqrt(norm()); }
};
struct l_t{
	p_t a, b;
};

double cross(p_t p,p_t q);
p_t line(p_t p,p_t q);

bool asc(p_t left,p_t right) {
    return left.x == right.x ? left.y < right.y : left.x < right.x;
}
int Crosspoint(l_t l,l_t m);

int main(){
  int n;
  cin>>n;
  for(int t=0;t<n;t++){
    p_t p,q,r,k,s;
    cin>>p.x>>p.y>>q.x>>q.y>>r.x>>r.y>>k.x>>k.y>>s.x>>s.y;
    l_t pq,qr,rp,ks;
    pq.a=p;
    pq.b=q;
    qr.a=q;
    qr.b=r;
    rp.a=r;
    rp.b=p;
    ks.a=k;
    ks.b=s;
    int ans=0;
    ans+=Crosspoint(pq,ks);
    ans+=Crosspoint(qr,ks);
    ans+=Crosspoint(rp,ks);
    if(ans==1){
      cout<<"OK"<<endl;
    }
    else{
      cout<<"NG"<<endl;
    }
  }
}


p_t line(p_t p,p_t q){
  p_t z;
  z.x=q.x-p.x;
  z.y=q.y-p.y;
  return z;
}


double cross(p_t p,p_t q){
  return p.x*q.y-p.y*q.x;
}

int Crosspoint(l_t l,l_t m){
  p_t aa,bb,cc,dd;
  aa.x=l.b.x-l.a.x;
  aa.y=l.b.y-l.a.y;
  bb.x=m.b.x-m.a.x;
  bb.y=m.b.y-m.a.y;
  cc=aa;
  dd.x=l.b.x-m.a.x;
  dd.y=l.b.y-m.a.y;
	double A = cross(aa,bb);
	double B = cross(cc,dd);
	if (abs(A) < EPS && abs(B) < EPS) return 0;
  if(B/A>0&&B/A<1) return 1;
  return 0;
}

C++: #include <stdio.h>
#include <iostream>
#include <vector>
#include <string>
#include <math.h>
#include <algorithm>
using namespace std;
#define INF 0x7FFFFFFF
const double EPS = 1e-10;


inline bool eq(double a, double b) { return fabs(b - a) < EPS;}

struct p_t{
  double x;
  double y;
  double norm() { return x * x + y * y; }
  double abs() { return sqrt(norm()); }
};
struct l_t{
	p_t a, b;
};

double cross(p_t p,p_t q);
p_t line(p_t p,p_t q);

bool asc(p_t left,p_t right) {
    return left.x == right.x ? left.y < right.y : left.x < right.x;
}
int Crosspoint(l_t l,l_t m);

int main(){
  int n;
  cin>>n;
  for(int t=0;t<n;t++){
    p_t p,q,r,k,s;
    cin>>p.x>>p.y>>q.x>>q.y>>r.x>>r.y>>k.x>>k.y>>s.x>>s.y;
    l_t pq,qr,rp,ks;
    pq.a=p;
    pq.b=q;
    qr.a=q;
    qr.b=r;
    rp.a=r;
    rp.b=p;
    ks.a=k;
    ks.b=s;
    int ans=0;
    ans+=Crosspoint(pq,ks);
    ans+=Crosspoint(qr,ks);
    ans+=Crosspoint(rp,ks);
    if(ans==1){
      cout<<"OK"<<endl;
    }
    else{
      cout<<"NG"<<endl;
    }
  }
}


p_t line(p_t p,p_t q){
  p_t z;
  z.x=q.x-p.x;
  z.y=q.y-p.y;
  return z;
}


double cross(p_t p,p_t q){
  return p.x*q.y-p.y*q.x;
}

int Crosspoint(l_t l,l_t m){
  p_t aa,bb,cc,dd;
  aa.x=l.b.x-l.a.x;
  aa.y=l.b.y-l.a.y;
  bb.x=m.b.x-m.a.x;
  bb.y=m.b.y-m.a.y;
  cc=aa;
  dd.x=l.b.x-m.a.x;
  dd.y=l.b.y-m.a.y;
	double A = cross(aa,bb);
	double B = cross(cc,dd);
	if (abs(A) < EPS && abs(B) < EPS) return 0;
  if(B/A>0&&B/A<1) return 1;
  return 0;
}