2.

program b2;
uses crt;
var R:real;
    cv,dt:real;
const pi=3.14;
Begin
    clrscr;
    write ('Nhap ban kinh R= ');readln(r);
    dt:=pi*r*r;
    cv:=2*pi*r;
    writeln('Dien tich hinh tron la: ',dt:2:2);
    writeln('Chu vi hinh tron la: ',cv:2:2);
    readln;
End.

3.

program b3;
uses crt;
var b:longint;
Begin
        clrscr;
        write('B = ');readln(b);
        writeln('Binh phuong ',b,' = ',sqr(b));
        writeln('Can bac hai ',b,' = ',sqrt(b):2:2);
        write('Lap phuong ',b,' = ',sqr(b)*b);
        readln
End.

4.

program b4;
uses crt;
var a:integer;
Begin
        clrscr;
        write('nhap so (m): ');readln(a);
        writeln(a,'m = ',a*100,'cm');
        write(a,'m = ',a*10,'dm');
        readln
End.