In one sentence, describe what the following article is about:

This may be easier said than done, but here are some tips:  A line. If you see a line on the graph that extends to infinity, then all versions of x will be covered eventually, so the domain is equal to all real numbers. A normal parabola. If you see a parabola that is facing upwards or downwards, then yes, the domain will be all real numbers, because all numbers on the x-axis will eventually be covered. A sideways parabola. Now, if you have a parabola with a vertex at (4,0) which extends infinitely to the right, then your domain is D = [4,∞) Just state the domain based on the type of graph you're working with. If you're uncertain and know the equation of the line, plug the x-coordinates back into the function to check.

Summary:
Look at the graph. Check out the x-values that are included in the graph. State the domain.