Question

Y = 2f(g(x))

dy/dx = 2f'(g(x)) * g'(x)
Differentiate again:
d^2y/dx^2 = 2f''(g(x)) * g'(x) * g'(x) + 2f'(g(x)) * g''(x)
d^2y/dx^2 = 2f''(g(x)) * (g'(x))^2 + 2f'(g(x)) * g''(x)
Am I correct in saying answer D?

Answer 1

Yes you used the chain rule properly to follow the correct steps to get the right answer. Great job.

If you wanted, you can come up with examples for f(x) and g(x) to help confirm the answer. A quick way to do this is to use something like GeoGebra to help graph the two expressions and you'll notice that the curves match up perfectly (indicating equivalent expressions). Note: GeoGebra can handle derivatives through the Derivative[] comand or you can type the function in the input bar with a tickmark after it to tell GeoGebra to derive the function.