I have been asked to see for what range of values provides a good approximation of , when I graph them with a window of and , the two lines look fairly close at the top, but I know that and .

I know that the lower limit of my answer is 0, but I can't figure out quite to find the upper limit. When I use the graph, do I look at differences in y values for specific x values, or differences in x values for specific y values?