$12^2.12^7$

$\frac{1}{1-\frac{1}{1-\frac{1}{1-cot^2a}}}=cot^2a$

$2x^2-2x-1$

$\left[3\left(x+4\right)-2\left(2x-3\right)\right]\left[\left(x+\right)-5\left(2x-3\right)\right]$

$\lim_{x\to1}\left(\frac{x^2+3x-18}{x^2-1}\right)$

$\left(\frac{1}{t^2}\right)\left(t\right)$

$ln\left(t^3\right)$