$\left(-25\right)\cdot\left(+40\right)\cdot0$

$-\frac{cos\left(2x\right)+1}{sin\left(2x\right)}$

$\frac{dy}{dx}=y\left(1+3x^2\right)$

$\frac{dy}{dx}+\frac{5y}{\left(1000+x\right)}=0.6$

$\lim_{x\to-1}\left(\frac{x^2+3x+2}{x^2+1}\right)$

$\frac{xy^2}{x^2y}$

$1+\frac{3}{x+4}=\frac{3}{x^2+9x+20}$