$$-19-\left(-12\right)+\left(-1\right)$$

$$9x-4.93xy+19y+38y-11x+19.75$$

$$sen\theta\:+tan\theta\:$$

$$\lim_{x\to0}\frac{x^2+1}{x^2-1}$$

$$\left(4x\:-\:y\right)^2$$

$$3^2.3$$

$$-4x^2-3xy+7+4x^2-5xy-3$$