triangle.lpr

program project1;

{$mode objfpc}{$H+}

uses
  {$IFDEF UNIX}{$IFDEF UseCThreads}
  cthreads,
  {$ENDIF}{$ENDIF}
  Classes, crt
  { you can add units after this };

var
  x1,x2,x3,x4,y1,y2,y3,y4,a,b,c,p,p1,p2,p3,S,S1,S2,S3,a1,b1,c1,Z,K,V: real;

begin
  writeln('Enter x1 and y1');
  read(x1,y1);
  writeln('Enter x2 and y2');
  read(x2,y2);
  writeln('Enter x3 and y3');
  read(x3,y3);
  begin
    a:=sqrt(sqr(x2-x1)+sqr(y2-y1));
    b:=sqrt(sqr(x3-x2)+sqr(y3-y2));
    c:=sqrt(sqr(x3-x1)+sqr(y3-y1));
    p:=(a+b+c)/2;
    S:=sqrt(p*(p-a)*(p-b)*(p-c));
    writeln('Enter x4 and y4');
    read(x4,y4);
    a1:=sqrt(sqr(x1-x4)+sqr(y1-y4));
    b1:=sqrt(sqr(x2-x4)+sqr(y2-y4));
    c1:=sqrt(sqr(x3-x4)+sqr(y3-y4));
    p1:=(a+a1+b1)/2;
    p2:=(b+b1+c1)/2;
    p3:=(c+a1+c1)/2;
    S1:=sqrt(p1*(p1-a)*(p1-a1)*(p1-b1));
    S2:=sqrt(p2*(p2-b)*(p2-b1)*(p2-c1));
    S3:=sqrt(p3*(p3-c)*(p3-a1)*(p3-c1));
    Z:=S1+S2+S3;
    K:=round(S*2)/2;
    V:=round(Z*2)/2;
        if (S1=0) and (S2=0)
    then writeln('Point belongs to an edge of the triangle')
    else
        if (S2=0) and (S3=0)
    then writeln('Point belongs to an edge of the triangle')
    else
        if (S1=0) and (S3=0)
    then writeln('Point belongs to an edge of the triangle')
    else
     if (S1=0) or (S2=0) or (S3=0)
    then writeln('Point belongs to the top of the triangle')
    else
    if (K=V)
    then writeln('Point belongs to the triangleЄг')
    else writeln('The point does not belong to the triangle')
  end;
    readkey;
end.