$3\left(\log x+\log y-2\log z\right)$

$1-\cos^2\left(70\right)$

$\frac{-x^4-4x^3+6x^2-7}{x^2-2}$

$x^2-18\le0$

$\frac{1}{\sec\left(a\right)-\tan\left(a\right)}-\frac{1}{\sec\left(a\right)+\tan\left(a\right)}=2\tan\left(a\right)$

$\frac{9x^6}{3x^2}$

$\frac{d}{dx}\left(\frac{1}{2}e^{-2x}-2\right)$