$x^2+4x+6=0$

$a^3b^6-512c^9$

$\:\:8x^2-26x-7$

$\left(a+3\right)\left(a-3\right)=a^2-9$

$log\left(\frac{x}{5}\right)=3$

$\cos\left(\frac{15}{17}\right)\cos\left(\frac{12}{13}\right)-\sin\left(\frac{15}{17}\right)\sin\left(\frac{12}{13}\right)$

$\lim_{x\to9}\left(\frac{5x+8}{x^2-81}\right)$