Question

what is a line graph

Answer 1

On the two-dimensional Euclidean plane, a "line graph" can be taken to be the graph of a function of the form \(f(x)=mx+b\).

Answer 2

This seems like an answer that probably is too technical for the scope of the question, so I'll try to explain it. The 2-dimensional Euclidean plane is pretty much something that is a flat surface like a piece of paper. 2-d means means it has 2 directions, x and y. A line graph is a straight line drawn on this flat surface. The line can be described in terms of algebra in the form f(x) = y = m*x+b, where m and b are constants that define the entire set of points of the line, and x describes a particular point on the line.