A generic line function is based on this format:
In this case, 2x + y = 5 we have to isolate 'y' to fill the format above:
a = -2 and b = 5. So that is a linear function. I will show to you other examples that are not linear:
These are not linear functions because they are not in the y = mx + b format! m and b can be any real number. If m is equal to zero, the function will be constant! Otherwise, if b is equal to zero, the function will be linear.