For which of the following functions f is f (x)= f (1-x) for all x?
A) f (x)= 1-x
B) f (x)= 1-x^2
C) f (x)= x^2 - (1-x)^2
D) f (x)= x^2 (1-x)^2
E) f (x)= x/ (1-x)
Backround humanities, don´t have a clue in this one. Help's much appreciated