Which type of equation is characterized by a graph that forms a straight line?

A linear equation is defined by its property of having a constant rate of change, which is reflected in its graph as a straight line. In mathematical terms, a linear equation is typically expressed in the form (y = mx + b), where (m) represents the slope and (b) is the y-intercept. This consistent slope means that for every unit increase in (x), there is a proportional increase (or decrease) in (y), resulting in a straight line.

The characteristics of linear equations can be seen in how they interact with the Cartesian coordinate system, where the graph will extend infinitely in both directions along the line. The simplicity of linear relationships makes them fundamental in algebra and calculus, serving as a basis for understanding more complex equations.

The other options refer to different mathematical concepts: slope pertains to the measure of steepness of a line but is not itself an equation, supplementary angles deal with angle relationships in geometry rather than equations, and the area of a rectangle involves calculations related to two-dimensional shapes, which does not relate to the type of equations that produce straight-line graphs. Thus, when the question specifically asks about the type of equation associated with a straight-line graph, the accurate answer is linear equation.