$\lim_{x\to0}\left(\frac{x^3+2x}{x^5}\right)$

$\left(+1\right)+\left(-7\right)+2.\left(+7\right)-3.\left(-3\right)$

$\frac{1}{4}\left(4x-8\right)-2\left(5x+6\right)$

$6a-3b$

$2n+\left(3n+1\right)\cdot\left(-2\right)$

$\sqrt{y}dy+\left(1+x\right)dx=0\:;\:y\left(0\right)=1$

$\int\left(x+e\cdot\right)^2$