Final answer:
An equation of the form y = a + bx, where a is the y-intercept and b is the slope, defines y as a function of x because each x corresponds to exactly one y.
Step-by-step explanation:
A function is a mathematical concept where each input (in this case, the independent variable x) has exactly one output (the dependent variable y). To determine whether the equation defines y as a function of x, you need to see if for every value of x, there is only one corresponding value for y. Based on the information provided, the equation in the form y = a + bx, where a is the y-intercept and b is the slope, clearly defines y as a function of x because for every x, there's a unique y.
Examples of linear equations that are functions include y = -3x, y = 0.2 + 0.74x, and y = -9.4 - 2x. These are all of the form y = mx + b and meet the criteria for a function.