Let f and g be differentiable functions such that fog=I, the identity function, If g′(a)=2 and g(a)=b, then f(b)=
-2
12
2
None
(fog)'(x)=x for all x⇒ (fog)'(a)=1 ⇒fgag'a=1⇒f(b)g'a=1⇒2f(b)=1⇒ f(b)=12.Hence (2) is the correct answer.