(a) Prove that Q(sqareroot 5)={a+b sqareroot 5 ; a,b in Z} is asubring of Z.
(b) Show that Q(sqareroot 5) is a conmutative ring.
(c) Show that Q(sqareroot 5) has a multiplicative identity.
(d) show that Q(sqareroot 5) is a field.(Hint : you want tomulitply something by he conjugate.)
(Abstract Algebra)
