$\frac{\left(7x^2\right)^3-\left(9y\right)^3}{7x^2-9y}$

$6+3\cdot\left(3-2\right)$

$-3\left[2\left(3-5+9-10\right)-4\left(2-7+9+5\right)\right]$

$\frac{dy}{dx}=\frac{xy-3x+6y-18}{xy+2x}$

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

$e^{3x}\frac{dy}{dx}=y^3$

$\tan\theta=\frac{\sec\theta}{\csc\theta}$