 Lines. Given an equation in variables \(x\) and \(y\), a point such as (2, 7) is said to be a solution to that equation when setting \(x\) to 2 and \(y\) to 7 makes the equation true. For example the equation \(y = 3x+5\) has as solutions the points (0, 5), (1, 8), (2, 11), and so on. Other solutions include (.5, 6.5), (1.5, 9.5), and so on. The set of all solutions constitutes the unique straight line passing through (0, 5) and (1, 8). We then call \(y = 3x+5\) the equation of that line.