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

$+162-343$

$\lim_{x\to\infty}\left(\sqrt{4x^2+1}-\sqrt{4x^2+x}\right)$

$\left(y\right)^'+\frac{y}{x}=x\sqrt{y}$

$\left(x+y\right)\frac{dy}{dx}=3$

$\frac{4}{3.6}$

$\left(3+i\right)\left(3-i\right)$