$$39x^2-30x+25$$

$$5\cdot\left(-3\right)+\left(-6\right)\cdot4+\left(-3\right)\cdot\left(-7\right)$$

$$2x+3=x-4$$

$$6z+8z^2+z+5z^2$$

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

$$9x-2x+3y$$