I expect the way you entered the function into your grapher has the computer reading the function as $\displaystyle \begin{align*} 2x + \frac{1}{2}x \end{align*}$ instead of $\displaystyle \begin{align*} 2x + \frac{1}{2x} \end{align*}$. Try entering the function as y = 2*x + 1/(2*x).

I expect the others are similar problems.