Thread: the derivative of sec[f(x)] ?

Originally Posted by sadieann

would it be: sec[f'(x)]tan[f'(x)] f'(x) ?

Close.

sec[f(x)]tan[f(x)]f'(x)

are you sure? that's not one of the choices on my homework

Originally Posted by sadieann

are you sure? that's not one of the choices on my homework

Yes. This is the basic idea of the chain rule. Let's say you have two functions, g(x) and f(x). d/dx g[f(x)] = g'[f(x)]*f'(x). What are the choices given?

The choices are:

sec[f'(x)]tan[f'(x)]

sec[f(x)]tan[f'(x)]f'(x)

sec[f'(x)]tan[f(x)]f'(x)

sec[f'(x)]tan[f'(x)]f'(x)

tan[f(x)]f'(x)

I don't know what to tell you. I'm 99% sure I'm right and only doubting myself because of this weird situation. Problems are incorrectly written all the time. Do you follow my reasoning? This is a basic application of the chain rule.