$\cos\left(x\right)-\cos\left(2x\right)=\cos\left(4x\right)$

$4\left(x+2\right)-20\left(x-6\right)$

$2x^2+4x-\frac{3}{x-5}$

$\int\frac{21x-15}{x^2-x-2}dx$

$\frac{\left(x^3+x+1\right)}{\left(x-1\right)}$

$\tan\left(x\right)-\tan\left(x\right)\sin\left(x\right)=0$

$\left(-6mx+4ng\right)^2$