$20-2yf^2;\:y=1;\:f=2$

$\log\left(x-16\right)=2-\log\left(x-1\right)$

$6\left(x+1\right)^{-1}\le3x^{-1}$

$\frac{x^2-4x+4}{x^2-x-12}$

$y'=e^{3x-4y},\:y\left(0\right)=0$

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

$\lim_{x\to1}\left(\frac{ln\left(ex\right)-1}{sin\left(\pi x\right)}\right)$