$x^2-4x+1,5$

$\left(k-8\right)\left(k+8\right)$

$4a^48a^2b^2+9b^4$

$\lim_{x\to\frac{\pi}{4}}\left(sec^2u+csc^2u\right)$

$\lim_{x\to1}\left(\frac{5-x^2}{sen\left(\pi x\right)}\right)$

$\frac{dy}{dx}=\frac{1}{y-x-1}$

$\frac{tan^2\left(x\right)}{sec\left(x\right)}=\frac{\left(sec^2\left(x\right)-1\right)}{sec\left(x\right)}$