Two integral problems including e and sin

[adimi24]

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.

Thanks in advance

 

[micromass]

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

\int{e^ydy}

 

[JHamm]

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

 

[adimi24]

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

\int{e^ydy}

Thanks, I figured out the first one.

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

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

 

[Bohrok]

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

-1/4 ∫ cos(pi x) - 3Ln| x|

...

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

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.

 

[adimi24]

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.

I think I just wrote -1/4 instead of -1/pi by accident. But I got help from a teacher so it's all good now.

Thanks for the help everyone.