$-x^2-x+y^2-y^2$

$\lim_{x\to999}\left(\frac{\sqrt{x}}{x+1}\right)$

$\lim_{x\to1}\left(\frac{3x-1}{x+1}\right)^{\frac{1}{2x-2}}$

$1x^3+4x^2+1x^1-6x^0$

$\frac{\sec x}{1}+\frac{\csc x}{\cot x}=\sec x$

$10\left(x^2\right)-20+20cos\left(x\right)$

$2-3\cdot\left(-5\right)^2$