Here's the question you clicked on:
ChrisV
Find the derivative of the trigonometric function. f(x)=-x+tanx
Well, the derivative of tanx = sec^2x. so.. \[f'(x) = -1 + \sec^2x\]
hmmmm how do i knw the derivative of tanx = sec^x?
y' =sec²x - 1 http://www.wolframalpha.com/input/?i=derivative+of+y+%3D-x+%2B+tan%28x%29
Well, you have to like memorise the derivative of it.
and the book says tan^2x so i assume sec^2x -1 = tan^2x
Yes. Its a trig identity.
oh i belive mimi just asking for my knowledge
dont want someone just doing my homework for me
id rather learn then just write down the correct answer :)
You have to know the basic trig identities. Just a few of them and they are related.
i am just wondering why my book doesnt tell me this before asking this question
oh i know the trig identities but not the derivatives
like i know 1-sin^2 = cos^2
but that didnt teach me the derivative of cos^2
thanks i looked at it :)
so i need to memorize these too?