$9x^2+2xy^2=-4$

$-\sqrt{15.9}$

$\lim_{x\to0}\left(\frac{x^2-9}{\sin\left(x-3\right)}\right)$

$\frac{-x^2}{x^2+1}$

$\lim_{x\to0}\left(\frac{ln\left(cos\left(x-2\right)\right)}{1-sen\left(\frac{\pi}{4\:}x\right)}\right)$

$\frac{x+5}{7x+2}-\frac{x-7}{5x+1}=7$

$\sqrt[3]{8a^2b^3}\cdot\sqrt[3]{2a^3b^5}$