Trigonometric Ratio and Identites

If $x = \sum\limits_{n = 0}^\infty {{{\left( { - 1} \right)}^n}{{\tan }^{2n}}\theta }$ and $y = \sum\limits_{n = 0}^\infty {{{\cos }^{2n}}\theta }$ for 0 < $\theta$ < ${\pi \over 4}$, then :