$$\left(2.59\right)\cdot\left(-30.6\right)$$

$$\left(\frac{x^2}{4}\right)+x^2$$

$$\lim_{x\to+\infty}\sqrt{2x^2+4}-\sqrt{5x^2-5}$$

$$81^2-90x+25$$

$$\lim_{x\to4}\left(\frac{2x^2+3x+1}{x^2-2x-3}\right)$$

$$4x+6\ge2x-3$$

$$4x^2y^2-8x^2b$$