$$y.\ln\left(x+1\right)-y\cos\left(xy\right)+y^x-\left(3x+y\right)^2+1$$

$$\frac{dy}{dx}\left(\frac{x^2}{y^2-6}\right)=\frac{1}{2y}$$

$$-2m^2n^6+-3mn^6$$

$$4ax^2+5ax^2$$

$$\lim_{x\to6}\left(\frac{x^3-216}{x^2-36}\right)$$

$$18z+4-13z$$

$$\lim_{x\to2}\left(\frac{x^4-16}{x^3-18}\right)$$