Răspuns:
program triunghi;
var xA,yA,xB,yB,xC,yC,p,aria,AB,AC,BC:real;
begin
Write('xA=');Read(xA);
Write('yA=');Read(yA);
Write('xB=');Read(xB);
Write('yB=');Read(yB);
Write('xC=');Read(xC);
Write('yC=');Read(yC);
AB:=Sqrt(sqr(xA-xB)+Sqr(yA-yB));
AC:=Sqrt(sqr(xA-xC)+Sqr(yA-yC));
BC:=Sqrt(sqr(xB-xC)+Sqr(yB-yC));
p:=(AB+BC+AC)/2;
aria:=Sqrt(p*(p-AB)*(p-BC)*(p-AC));
Writeln('aria=',aria);
end.
Explicație: