Use the chain rule to differentiate both sides of the given equation with respect to [tex]x[/tex] :
[tex]y = 2 f(g(x))[/tex]
[tex]\dfrac{dy}{dx} = y' = 2 f'(g(x)) g'(x)[/tex]
Differentiate again with the product and chain rules to get the second derivative :
[tex]\dfrac{d^2y}{dx^2} = y'' = \boxed{2 f'(g(x)) g''(x) + 2 f''(g(x)) g'(x)^2}[/tex]
(D)
