$\left(y-6\right)\left(y+7\right)$

$\frac{d}{dz}\left(\frac{\sin\left(3z+z^2\right)}{\left(6-z^4\right)^3}\right)$

$\lim_{x\to\infty}\left(x^{-\frac{1}{x}}\right)$

$\left(x^a-y^{2a}\right)^2$

$19+3^4-6-\left(-3+9\right)^2$

$-12-y\:y=19$

$\frac{tgx+\frac{1}{cosx}.cscx}{tgx+\frac{1}{cosx}.cscx}$