HP 50G help

[jrmc114064]

I've had my 50G for about a year now and use it heavily, recently I have been working on problems that incorporate variables within the integral and am having trouble as it seems each time I take the antiderivative it throws up a undefined name error. I was hoping to get some help, an example problem would be:

int(ax^2-4,x)

How would you account for the variable a? Thanks for your time, really do appreciate it, and I know my syntax is wrong for my example in advance