$-168,7+204,513+346-254187$

$\lim_{x\to0}\left(\frac{x^2-1-\ln\left(x\right)}{\left(\ln\left(x\right)\right)\cdot\left(x^2-1\right)}\right)$

$\lim\:_{x\to\:\infty\:}\left(1+\frac{6}{x^3}\right)^{x^3}$

$\tan\left(2x\right)^2.\sec\left(2x\right)^2$

$\left(\frac{a^3}{64}-\frac{b^3}{343}\right)$

$\:6b^2-23b+21$

$\lim_{x\to0}\left(\frac{1-2x}{x^2}\right)$