Let $\displaystyle U = \mathbb{R}^2 \setminus \{(0,0)\}$; consider the $\displaystyle 1-$form in $\displaystyle U$ defined by

$\displaystyle \omega = \dfrac{x dx + ydy}{x^2+y^2}$

(a) Show that $\displaystyle d\omega =0$

(b) Show that there is a $\displaystyle 0$-form $\displaystyle \theta$ on $\displaystyle U$, such that $\displaystyle d\theta = \omega$

Please help!!!