please help, some basic programming

[pegasus9679]

Hi,

I don't have any experience programming the 89, but I did take a college course on C++ so I know a little about programming.

For some reason, my 89's d( function does not follow the product rule. Please tell me step by step how to kinda hack into the function and fix the code.

And is this a problem for anyone else or just for me? I thought I could trust my 89. If I didn't figure this out I would have let it differentiate everything for me in the exam.