Hey Everyone,

I am new to TI-BASIC programming, as I just received my TI NSpire. I attempted to Define a variable to make an easier of way of finding the 'numerical derivative at a point'. The current way is Menu- Calculus- numerical derivative at a point - then you get a window - then you get a template. I attempted to make a way for doing this quickly, however it did not work. Can someone please find the flaws in my following program:

Define d(a,y)= d/dx (a)|x=y.

However, when I attempt to apply this by doing d(x^2,4) the calculator says: "Error Variable is not Defined".

Sorry if this is a stupid question, but can you please help :)