$\frac{\sin x}{\cos x}+\frac{\cos x}{\sin x}=\sec x\cdot\csc x$

$\lim_{x\to0}\left(\frac{4x}{\sqrt{4+x}-\sqrt{4-x}}\right)$

$-8m\left(3\right)$

$ca^{3}-a+a^{2}\right)\left(a-1\right)$

$-25x^4y^2-121$

$n=e^{xy}+c$

$\cos\left(2x\right)=\frac{1-\tan\left(x\right)^2}{1+\tan\left(+\right)^2}$