Skip to content

The function f is defined by

f(x)=(x+2)(x−1)

Find all possible values of x such that the sequence defined by

u1=xun+1=f(un)

is periodic of period 2.


We need u1=u3, which implies

f(f(x))=x

The equation

f(f(x))=x

has 4 solutions, but only two of these are valid.