$2cosx\:-\:sinx\:=\:\frac{3}{\left(2cosx+sinx\right)}$

$\lim_{x\to2}\left(\frac{x^2-1}{\sqrt{x}-1}\right)$

$\left(1-5\cos\left(2x\right)\right)$

$\lim_{x\to\infty}\frac{\cos\left(x\right)}{\sin^2\left(0\right)}$

$-a^2+3ab+b;\:a=3;\:b=-2$

$\frac{8x^2-81}{6^4-4^2}$

$x^2-24x=c$