$21x^2+9$

$\left|\left(3a-4b\right)\left(a+b\right)\right|-\left|\left(a+2b\right)\left(a-b\right)\right|$

$\lim_{x\to0}\left(\frac{\ln\left(x+1\right)}{\ln\left(3+x^2\right)}\right)$

$\lim_{x\to0}\left(-5\right)$

$\int\frac{\sqrt{64-x^2}}{x^2}dx$

$3\left(4x+4\right)$

$\left(x+3\right)\left(x^2+3x+9\right)$