$$x^2+16xy+64y^2$$

$$2x^2-72x=0$$

$$sec\:x\:\frac{dy}{dx}=e^y$$

$$\cos\left(x-2\pi\right)-\cos\left(2\pi\right)$$

$$4-\infty$$

$$\frac{d}{dx}\left(x^6sin^2\left(2x\right)\right)$$

$$\left(x^2-y^2\right)-\left(x-y\right)^2$$