2:
uses crt;
var a,b,c,p,s:real;
begin
clrscr;
write('Nhap a='); readln(a);
write('Nhap b='); readln(b);
write('Nhap c='); readln(c);
if (a+b>c) and (a+c>b) and (b+c>a) and (a>0) and (b>0) and (c>0) then
begin
p:=(a+b+c)/2;
s:=sqrt(p*(p-a)*(p-b)*(p-c));
writeln('Dien tich tam giac la: ',s:4:2);
end
else writeln('Vui long nhap lai');
readln;
end.