# What's the indefinite integral?

1. Aug 19, 2008

### afcwestwarrior

of sin pi x dx

i thought it would be - cos pi x dx but i think it might be (1/pi) -cos pi x dx

2. Aug 19, 2008

### Anthony

$$\int \sin (\pi x)\, \mathrm{d}x =\frac{1}{\pi} \int \sin (\pi x) \, \mathrm{d} (\pi x)$$

Does this help?

3. Aug 19, 2008

### afcwestwarrior

yea a lot thanks, i guessed right but i didn't know if i was right

4. Aug 19, 2008

### afcwestwarrior

just wondering why is it 1/pi, i'm not even sure why

5. Aug 19, 2008

### HallsofIvy

Staff Emeritus
What is the derivative of cos(pi x)?

6. Aug 19, 2008

### afcwestwarrior

it's - sin (pi x)

7. Aug 19, 2008

### NoMoreExams

To integrate $$sin( \pi x) dx$$ consider doing a substitution of $$u = \pi x$$ then substitute in the appropriate expression of dx in terms of du.

8. Aug 20, 2008

### HallsofIvy

Staff Emeritus
Well, there is you problem then: it isn't. Use the chain rule.

Last edited: Aug 20, 2008