Glad to know that was helpful – thanks!
- There are certain questions, like this one, whose maxima and minima can only found using a GDC?
Absolutely. Any function whose first derivative results in an equation that can’t easily be solved to find the critical points will require a numerical method (which you probably don’t know yet), or a computer/calculator to help, which could be a graphing display calculator (GDC). When most students are learning Calculus they’re only given functions that result in first derivatives that can be solved by factoring or some other relatively straightforward technique, so you’d naturally conclude all functions work this way . . . but actually the problems have been crafted so things work out that way. In “the real world” there’s no guarantee that that will be the case.
- How do you create a dotted line for the function outside the domain? I used desmos and it just darkens the area.
We created a second expression for the region outside the stated domain, and made that curve dotted with the same color. (Just wanted to make sure everyone could get a visual sense for the horizontal asymptotes being zero.)
- How do I use the insert equation feature? I clicked on it, but I do not see a box coming up as in word. \frac{1}{x}. I used 1/x just as a trial.
Sorry about that, and thanks for letting us know. A recent update to the Forum software probably introduced an error; we’ll investigate and get that fixed. In the meantime, if you’re comfortable writing LaTeX, if you put a single dollar sign $ around both sides of the equation, like $\frac{1}{x},$ you’ll get \frac{1}{x}. You can see more about the usage on our Forum here: How to typeset an equation
- I got my error while finding the derivative. I used quotient rule and used it as 1/sqrt(1+x^2) instead of using it as sqrt(1+x^2).
Glad you found that! It’s the most common error when using the Quotient Rule, and most of us have to make it a few times early on before the correct approach become automatic. So, glad you did that now rather than later on an exam. 
Please let us know how else we can help!