Using SLOPE function in Function APP with CAS defined function

[cdecastro]

Here's a little problem I encountered with SLOPE.

in CAS, enter,

f(x):=x^2

then go to the Function App and enter f(X) to graph. Now try to obtain the slope using the SLOPE function and the calculator reports NaN.

FYI: The SLOPE function does work if I enter F1(x) = X^2 in the Function App and find the slope.

Thanks,
Chris