hey guys

having a problem with a couple of calculus proofs...please help!

(1) prove that $\displaystyle n$ is odd iff $\displaystyle n^2$ is odd

i have done the <--- part of this, im just having a problem proving that $\displaystyle n$ is odd if $\displaystyle n^2$ is odd (the ---> part)

(2) Show that there exists no rational number $\displaystyle x$ such that $\displaystyle x^2$ = 3.

i have attempted to use proof by contradiction but im getting nowhere!

thanks