# Homework Help: Derivative of a trig. function

1. Jul 14, 2012

### frosty8688

1. Find the derivative of the function using the power rule or product rule

2. sinθ/2 + c/θ

3. I tried to do plus or minus the √1-cosθ/2

2. Jul 14, 2012

### eumyang

Your question is ambiguous. Please use parentheses. It looks like that want to find the derivative of
$$\frac{\sin \theta}{2} + \frac{c}{\theta}$$

3. Jul 14, 2012

### frosty8688

Yes, that's it

4. Jul 14, 2012

### Saitama

There is no need to plus or minus the √1-cosθ/2, simply find the derivative of sin θ and 1/θ w.r.t θ (I suppose that's what you are asked.) And what about c? How is it defined in the question?

5. Jul 14, 2012

### frosty8688

Here's what I have (cosθ/2) + (c/θ). c is a variable.

Last edited: Jul 14, 2012
6. Jul 14, 2012

### e^(i Pi)+1=0

The c probably stands for some constant.

7. Jul 14, 2012

### frosty8688

ok, thanks.

8. Jul 14, 2012

### eumyang

If c is a constant, and the above is your solution attempt, then you have to do something with the 2nd term (ie. the derivative of c/θ isn't c/θ).

9. Jul 14, 2012

### frosty8688

The solution would be (cosθ/2).

10. Jul 14, 2012

### Saitama

No, how do you get this? What's the derivative of 1/θ?

11. Jul 14, 2012

### frosty8688

The derivative of a constant is 0.

12. Jul 14, 2012

### eumyang

Sorry, that's wrong. If the original problem was this:
$$\frac{\sin \theta}{2} + c$$
(with c as a constant), then your answer would be right. But the 2nd term has a θ in the denominator. What do we do?

13. Jul 14, 2012

### frosty8688

It would be (cosθ/2 - c/θ^2)

14. Jul 14, 2012

Looks good.