# Homework Help: Derivatives of trigonometric functions

1. Jul 28, 2008

### Brunno

1. The problem statement, all variables and given/known data
I'm learning now about darivative all by my self (without a teacher) and I'm not sure about this development

2. Relevant equations

3. The attempt at a solution

$$Y=senx$$

$$y+{\Delta}Y=sen(x+{\Delta}Y)$$

$${\Delta}Y=senx*cos{\Delta}x+ sen{\Delta}x*cosx$$

What about this cos,what is it doing in the equation?
I really don't get it.

2. Jul 28, 2008

### Kushal

Re: Derivative

this comes from the double angle formula.

it says that: sin (A + B) = sinAcosB + sinBcosA

you can find the same thing for sin (x + dY)

3. Jul 28, 2008

### Brunno

Re: Derivative

Oh,now I think i get it!
Thankyou!

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook