# Homework Help: Two integral problems including e and sin

1. Sep 6, 2011

1. ∫ 6e^(-y/4) dy

2. ∫ [ sin(pi x) - (3/x) ] dx

Any help with either of these would be great. I'm teaching myself integrals for Physics C and i have absolutely no clue what to do with these.

2. Sep 6, 2011

### micromass

For the first one: factor ou the 6 and find a suitable substitution to bring the integral back to

$$\int{e^ydy}$$

3. Sep 7, 2011

### JHamm

For the second one you can separate it in to two integrals, sin(pi x) dx and -3/x dx

Last edited: Sep 7, 2011
4. Sep 7, 2011

Thanks, I figured out the first one.

But am still confused with this one. So far i have :

-1/4 ∫ cos(pi x) - 3Ln| x|

These were actually both definite integrals I was supposed to evaluate..so when I evaluated -1/4 ∫ cos(pi x) - 3Ln| x| from 10 to 2 I was within 6 tenths of the right answer. Is the answer sheet wrong or what did i do wrong?

Also, this may be a silly question but am I supposed to use pi as in 3.14 or 180

5. Sep 7, 2011

### Bohrok

How did you get -1/4 ∫cos(pi x) ?

x is probably in radians, so you'll use 3.14 instead of 180 for degrees.

Last edited: Sep 7, 2011
6. Sep 7, 2011