A cool derivative

Calculus Level 2

Which of the following answer choices shows the derivative of an odd function and an even function respectively?

even function and odd function odd function and odd function odd function and even function even function and even function none of the above

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2 solutions

Akhil Bansal
Jul 13, 2015

Let f(x) be a given real valued function and E(x)=f(x)+f(-x) and O(x)=f(x)-f(-x).
Clearly E(x) and O(x) are respectively even and odd functions.
Now,E'(x)=f'(x)-f'(-x) which is an odd function and O'(x)=f'(x)-(-f'(-x))=f'(x)+f'(-x) which is an even function.

what about |x|? derivative doesn't exist for this function at x=0.I think none of the above will be answer.

Saurabh Shree - 5 years, 9 months ago

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Something like this should be ignored anyway.

Paul Paul - 5 years, 8 months ago

Rather than simply solving it visually as I did you actually proved with a general example why this is true, nice!

Paul Paul - 5 years, 10 months ago

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hi paul .Since it is a generalised question the answer should consider all the possibilities.Merely ignoring the possibility to match the options is not the best approach.

Saurabh Shree - 5 years, 8 months ago

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I was actually lazy in solving the question so I took a sample which pinpointed only one correct answer. If in general there was something else then no answer would have been correct. This shows less about my knowledge in maths (which isn't perfect) and more about, uhm, you decide :))

Paul Paul - 5 years, 8 months ago
Nalini Nema
Aug 9, 2015

f'(sinx)=cosx And f'(cosx)=-sinx...So,even and odd function respectively.

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