Checking correctness... I'm missing something

I have a problem where students are evaluating the derivative of a function with a constant “k” involved, using check marks and x’s as the suffix to tell them if they got it or not. I want it to not matter how they type the answer in (beyond being correct and using the correct variables involved), but I only get my check mark if I typed it exactly as I did in the CL. Can someone give me a better way for handling this?

Here’s the activity (or the slide I’m working on, anyway…)

How’s this? This is another method using a graph. It can be pretty robust because you can use lists to make a lot of comparisons.

That will work perfectly. Thank you so much!