Which equation represents the formula of a straight line?

The equation that represents the formula of a straight line is given by (y = mx + c). In this equation, (m) stands for the slope of the line, which indicates how steep the line is, while (c) represents the y-intercept, the point where the line crosses the y-axis. Thus, this formula allows for the full representation of a linear relationship, as it takes into account both the slope and the starting point on the y-axis.

In comparison, other options either do not represent a straight line or are incomplete representations. For instance, (y = ax^2 + b) represents a quadratic function, which forms a parabola rather than a straight line. The equation (y = m + bx) is not a standard format for a linear equation as it confuses the roles of slope and intercept, making it less clear. The equation (y = mx) represents a specific case of a straight line that passes through the origin, but it lacks the y-intercept term, which limits its general applicability. Only (y = mx + c) maintains the full generality necessary to describe any straight line in a Cartesian coordinate system.