$\frac{\cot\left(-t\right)+\tan\left(-t\right)}{\cot\left(t\right)}=-\sec^2\left(t\right)$

$8n-\left(5n+8\right)=4$

$\sqrt{xy-x}$

$\int\left(\frac{6}{4-x^2}\right)dx$

$\left(3x-2\right)^2=9x^2-6x+4$

$0.5\left(d-2\right)=-0.2\left(d+19\right)$

$-\left(a-b\right)^2+\left(a+b\right)^2-3ab$