помогите

uses crt;
var a,b,c,x1,x2,d:real;

begin
    clrscr;
    write('a=');readln(a);
    write('b=');readln(b);
    write('c=');readln(c);
    d:=sqr(b)-4*a*c;
    x1:=(sqrt(d)-b)/2*a;
    x2:=(-sqrt(d)-b)/2*a;
    writeln('x1=',x1);
    writeln('x2=',x2);
    readkey
end.

var x3,q:longint;s:string;c:integer;
begin
for x3:=100 to 999 do
begin
str(sqr(x3),s);
s:=(copy(s,length(s)-2,3));
val(s,q,c);
if q=x3 then write(x3:4);
end;
readln;
end.

uses crt;
var n,i:integer;
      result:real;
begin
writeln('Enter N');
readln(n);
result:=1;
for i:=2 to n do
result:=result*(1+1/(n*n));
writeln('n=',n);
readln;
end.