# Homework Help: I don't understand the meaning of f^(39)(pi/2)?

1. Oct 6, 2011

### jrjack

I don't understand the meaning of f^(39)(pi/2)??

1. The problem statement, all variables and given/known data

Find the indicated derivative of f(x)=sin x and evaluate it at x=pi/2.

$$f^{(39)}(\pi/2)=$$

2. Relevant equations

3. The attempt at a solution

I'm not sure what the f^39 means??? And it could be f(39)(pi/2)??? but it looks like f raised to the 39th power???

Is this a common way to express a problem, because I have not seen one like this yet?

I know the derivative of sin x, is cos x, and if x=pi/2, then cos(pi/2)=0

But how should I evaluate the rest of this problem?
If f^(39) makes no sense, then f(39)(pi/2) doesn't make any sense, because x=pi/2???

2. Oct 6, 2011

### physicsnewb7

Re: I don't understand the meaning of f^(39)(pi/2)??

I think they mean take the 39th derivative of sin(x) and evaluate that at pi/2 the 2nd derivative -sin(x) third is -cos(x) and fourth is sin(x)......

Last edited: Oct 6, 2011
3. Oct 6, 2011

### jrjack

Re: I don't understand the meaning of f^(39)(pi/2)??

That makes more sense.

Is there a short cut or should I just change sin and cos (including the negative) 39 times?

4. Oct 6, 2011

### physicsnewb7

Re: I don't understand the meaning of f^(39)(pi/2)??

every fourth derivative gives you sin(x) I think you can take it from there

5. Oct 6, 2011

### jrjack

Re: I don't understand the meaning of f^(39)(pi/2)??

Yes, as I started doing it, I quickly saw sin x after 4 times, and ended up with -cos x = 0.

Thanks.

6. Oct 7, 2011

### Staff: Mentor

Re: I don't understand the meaning of f^(39)(pi/2)??

That's the right value, but what you got was -cos(π/2) = 0.

The notation f(39)(x), with parentheses around the exponent, usually means the derivative of that order. Without parentheses it would just mean raising the function to the indicated power.

7. Oct 7, 2011

### jrjack

Re: I don't understand the meaning of f^(39)(pi/2)??

Thanks for the clarity. Yes for this equation x = pi/2.