Question

derivative of cos(4x)

Answer 1

and what is the value of the derivative at x=pi/4

Answer 2

The derivative of cos is -sin. It's just something to remember. Therefore, the derivative of cos4x is -sin(4x). Just plug in pi/4 for the answer. Tell me what you got and we'll compare answers.

Answer 3

http://www.sosmath.com/calculus/diff/der03/der03.html

Answer 4

i got 0

Answer 5

btw isnt the derivative -4sin4x

Answer 6

Ah! Sorry about that, I had a typo.

Answer 7

I got 0 as well.

Answer 8

okay, can u take me thru the steps of this question:

Answer 9

have to find derivative of that.

Answer 10

its okay, i got it

Answer 11

Outer function:sin^2
inner function: sqrt t

D sin^2 * sqrt t * D sqrt t

sin(2x) * sqrt t * (1/2)sqrt t

sin(2x) * t/2

(t/2)sin(2x)

Answer 12

is the derivative of 2cosx, -2sinx?

Answer 13

Yep!

Answer 14

um, y=sinx - cosx

Answer 15

is the derivative cosx+sinx?

Answer 16

yes