$\left(6a+10b\right)\left(6a-10b\right)$

$sen^2x\left(1+\cot\left(x\right)\right)=1$

$\frac{3n+15}{4n^2}=\frac{1}{n^2}-\frac{n-3}{4n^2}$

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

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

$72\cdot1000$

$\sec x\csc x-2\cos x\csc x$