Answer:
Diagonal and horizontal lines
Step-by-step explanation:
To answer this question it is first important to know what a function is. A function is a relationship that has a singular y value for each x-value. This means that x-values will never repeat.
Linear functions are functions that increase in a constant way. Meaning that the slope of the line is constant and there is a common difference between the points. Because the change is constant, there is no change in direction. Thus, the function will be one straight line.
This line can obviously be diagonal because a diagonal line has unique x and y values. However, the line can also be horizontal. Horizontal lines many have repeating y-values but because the x-values don't repeat it is still a function. This reason is also why vertical lines are the only straight line to not be a liner function. In vertical lines, the x-values repeat. So, it does not work as a function.
