Question about CAS and Graphing

[Angus]

"This is unnecessary. In CAS, simply type:
F1:=f('X');
which evaluates f at the symbolic value 'X' and properly provides a formula for F1."


Does that work for you guys?
Type F1:=f('X') as advised. But when switching to function app I see a Syntax Error displayed for F1(X).
Checking the function gives 'x(X)^2'/2...

Trying Function.F2:=f('X'). Again there is a syntax error for F2(X) in the function app and the formula displayed when tapping that error id 'x(0)^2'/2.



Can someone point out what is wrong?