If the function y = xa − 31 is a linear function, what is the value of a? 1 2 3 4

If we are to assume that a is an exponent on the x, then a would have to be 1, because x^1 is the same thing as just plain old x.  If we put an exponent other than a 1 on that x, it is no longer linear.  If we put an exponent of 2, the function would be a quadratic.  If we put an exponent of 3, the function would be a cubic.  If we put an exponent of 4, the function would be a quartic.  Linear is just a plain line in the form y = mx + b.

What are the choices