Match the function with one of the graphs below using horizontal asymptotes as an aid.
f(x) = 4x/sqrt(x^2+2)
How to know that it's this graph
http://i.imgur.com/GVQls9u.png
or this graph
http://i.imgur.com/bdyfILn.png

Question

directrix · Answer

Because you know the graph is one of the two, I would go "low tech" and test a point. If x = 2, y = f(x) = (4*2)/(sqrt(2^2+2)) which is positive. That means that the graph has a presence in Quadrant I. So, look at the two graphs and select that option. 
@dangbeau