uses crt;
var a,b,c,d:longint;
begin
clrscr;
   write('Nhap a: ');readln(a);
   write('Nhap b: ');readln(b);
   write('Nhap c: ');readln(c);
   d:=sqr(b)-4*a*c;
   if (d<0)or(a=0) then writeln('Phuong trinh vo nghiem') else
   if d=0 then writeln('Phuong trinh co nghiem kep: x1=x2=-(b/(2*a))=',-(b/(2*a))) else
   if d>0 then 
      begin
         writeln('Phuong trinh co 2 nghiem phan biet: ');
         writeln('x1=(-b+sqrt(delta))/2*a=',(-b+sqrt(d))/2*a:0:2);
         writeln('x2=(-b-sqrt(delta))/2*a=',(-b-sqrt(d))/2*a:0:2);
      end;
readln;
end.

* Cách 1 : dùng lệnh đơn

uses crt;
var a, b, c, d : real;
begin
clrscr;
write('nhap he so a, b, c :');readln(a, b, c);
d := b * b - 4 * a * c;
if d < 0 then writeln('phuong trinh vo nghiem') else 
if d > 0 then writeln('x1 = ', (-b + sqrt(d)) / (2 * a):3:1,' x2 = ', (-b - sqrt(d)) / (2 * a):3:1) else
if d = 0 then writeln('x1 = x2 = x = ', (-b / (2 * a)):3:1) else
readln
end.

* Cách 2 : dùng câu lệnh ghép 

uses crt;
var a, b, c, x1, x2, d : real;
begin
clrscr;
write('nhap lan luot he so a, b, c :'); readln(a, b, c);
d := b * b - 4 * a * c;
if d > 0 then
begin
x1 := (-b + sqrt(d)) / (2 * a);

x2 := (-b - sqrt(d)) / (2 * a);

writeln('x1 = ', x1:3:1);

writeln('x2 = ', x2:3:1);
end
else
if d = 0 then writeln('x1 = x2 = x = ', (-b / (2 * a)):3:1)
else
writeln('phương trinh vo nghiem');
readln
end.