Let `f` be a real-valued function defined on the inverval `(-1,1)` such that `e^(-x)f(x)=2+int_0^xsqrt(t^4+1)dt ,` for all, `x in (-1,1)a n dl e tf^(-1)` be the inverse function of `fdot` Then `(f^(-1))^'(2)` is equal to 1 (b) `1/3` (c) `1/2` (d) `1/e`