## ChrisV 3 years ago Find the derivative of the trigonometric function. f(x)=-x+tanx

1. Mimi_x3

Well, the derivative of tanx = sec^2x. so.. \[f'(x) = -1 + \sec^2x\]

2. ChrisV

hmmmm how do i knw the derivative of tanx = sec^x?

3. Directrix
4. Mimi_x3

Well, you have to like memorise the derivative of it.

5. ChrisV

and the book says tan^2x so i assume sec^2x -1 = tan^2x

6. Mimi_x3

Yes. Its a trig identity.

7. ChrisV

oh i belive mimi just asking for my knowledge

8. ChrisV

dont want someone just doing my homework for me

9. ChrisV

lol

10. ChrisV

id rather learn then just write down the correct answer :)

11. Directrix

You have to know the basic trig identities. Just a few of them and they are related.

12. ChrisV

i am just wondering why my book doesnt tell me this before asking this question

13. ChrisV

oh i know the trig identities but not the derivatives

14. ChrisV

like i know 1-sin^2 = cos^2

15. Directrix
16. ChrisV

but that didnt teach me the derivative of cos^2

17. ChrisV

thanks i looked at it :)

18. ChrisV

so i need to memorize these too?