1.
program phuongt;
uses crt;
vaar a, b, c, dt: integer;
begin
clrscr;
write('Nhap a = '); readln(a);
write('Nhap b = '); readln(b);
write('Nhap c = '); readln(c);
dt:=0;
if (a = 0) and (b = 0) and (c = 0) then writeln('Phuong trinh co vo so nghiem');
if (a = 0) and (b = 0) and (c <> 0) then writeln('Phuong trinh vo nghiem');
if (a = 0) and (b <> 0) then writeln('Phuong trinh co nghiem: ', -c/b:2:1);
if (a <> 0) then
begin
dt:=b*b-4*a*c;
if dt<0 then writeln('Phuong trinh vo nghiem');
if dt=0 then writeln('Phuong trinh co nghiem kep la: x1 = x2 = ',-b/(2*a):2:1);
if dt>0 then writeln('Phuong trinh co 2 nghiem: x1 = ', (-b-sqrt(a))/(2*a):2:1, '; x2 = ', (-b-sqrt(dt))/(2*a):2:1);
end;
readln
end.
2.
program phuongt;
uses crt;
var a, b: integer;
begin
clrscr;
write('Nhap a = '); readln(a);
write('Nhap b = '); readln(b);
if (a = 0) and (b = 0) then writeln('Phuong trinh co vo so nghiem');
if (a = 0) and (b <> 0) then writeln('Phuong trinh vo nghiem');
if a <>0 then writeln('Phuong trinh co nghiem: x = ', -b/a:2:1);
readln
end.
3.
program phuongt;
uses crt;
var n, i, d: integer;
begin
clrscr;
write('Nhap n ='); readln(n);
d:=0;
if n>=2 then
begin
for i:=2 to trunc(n/2) do if n mod 1 = 0 then d:=d+1;
if d=0 then write(n, ' la so nguyen to')
else write(n, ' khong phai la so nguyen to');
end
else write('Nhap sai!');
readln
end.
