Determine best-fit curve and its function [y=f(x)] from multiple (x, y) data points in Excel

Hello,

This is a combined math and Excel question.

Given multiple (x, y) data points in a spreadsheet, how do you determine the curve that most closely represents the data points as well as the algebraic function of that curve?

For example, the following screenshot shows a set of 12 data points plotted as a scattergram:


In this particular case, the chart looks like the x-y relationship could be linear.  However, I assume a straight line function can be determined for any set of points no matter how dispersed.  Is that correct?  If so, does that mean there are two methods for determining best-fit curves, one linear and one nonlinear?

I'm familiar with the general linear equation (y = mx + b) and how to obtain it from two points but what method is used when more than two points are present (and they do not reside on a common line)?  Does it require integrals?

Also, does Excel have functions which provide solutions for the same questions?

Thanks

File attached
x-y-data-points_EE-2017-04-04.xlsm