a) var a,b,S : real ;
begin
write('nhap chieu dai'); readln(a);
write('nhap chieu rong'); readln(b);
S:=a*b ;
write('dien tich la',S);
readln
end.
b) var r,S : real ;
begin
write('nhap ban kinh'); readln(r);
S:=r*r*3.14 ;
write('dien tich la',S);
readln
end.