If 
then show that f [f{f(x)}] = x.
Given: 
Need to prove: f[f{f(x)}] = x
Replacing x by f(x),
⇒ 
Now again replacing x by f(x) we get,
⇒ 
⇒ 
⇒ 
[Proved]
1
If then show that f [f{f(x)}] = x.
Given:
Need to prove: f[f{f(x)}] = x
Replacing x by f(x),
⇒
Now again replacing x by f(x) we get,
⇒
⇒
⇒ [Proved]