Given h(x)=f(f(x))
⇒h′(x)=f′(f(x)).f′(x)
⇒h′(x)=f(f(x)).f(x)...(1) (as f′(x)=f(x))
Now f′(x)=f(x)
⇒f(x)f′(x)=1
Integrating both sides with respect to x, we get
ln∣f(x)∣=x+c
⇒f(x)=k.ex
⇒f(x)=e2.ex...(2)[∵f(1)=2]
Putting x=1 in equation (1), we get
h′(1)=f(f(1)).f(1)=f(2).2=2.e2e2=4e (using equation (2))