The Student Room Group

Integration help (any help is better than none!)

I'm only asking this here because I can't think of anyone else I can possibly ask, so hopefully someone can help me.
I always thought I was good at maths, but obviously not.

Anyway, there are two questions I'm struggling with.

1)Evaluate ∫(cosπx/2)dx with limits from 0-1

2) Evaluate
∫dx/(x+1)^1/2 with limits from 0-3

The first one has me completely lost, like I genuinely have no idea where to begin, we've never been shown anything like that in class.

The second one has me a bit baffled, but also wondering if it's a typo or just another way of typing "with respect to x," however I've never seen it written with the dx as the numerator and everything else as the denominator.

If anyone can help with anything, then you'd be a life saver because I'm about to crack my head off of a wall.

Scroll to see replies

Reply 1
Is the first one

cos(πx2)dx\int \cos (\frac{\pi x}{2}) dx

If so try differentiating sin(πx2)\sin (\frac{\pi x}{2})
(edited 11 years ago)
Reply 2
Original post by TenOfThem
Is the first one

cos(πx2)dx\int \cos (\frac{\pi x}{2}) dx

If so try integrating sin(πx2)\sin (\frac{\pi x}{2})

Yeah that's the first one, although I'm going to make myself sound like an idiot here,
1) how would integrating sin(πx/2) help with cos(πx/2)?
and 2) I still don't know how I'd even go about doing that. It's the πx/2 that's throwing me off. I'm sure it's really simple once I know how, but my issue is that I don't know how to start with, haha. Urgh I feel so stupid trying to figure this out!
Reply 3
Original post by angelooo


1) how would integrating sin(πx/2) help with cos(πx/2)?
!


ooops see edit
Reply 4
Original post by angelooo

It's the πx/2 that's throwing me off.


Can you do cos(3x)dx\int \cos (3x) dx as the method is the same
Original post by angelooo
Yeah that's the first one, although I'm going to make myself sound like an idiot here,
1) how would integrating sin(πx/2) help with cos(πx/2)?
and 2) I still don't know how I'd even go about doing that. It's the πx/2 that's throwing me off. I'm sure it's really simple once I know how, but my issue is that I don't know how to start with, haha. Urgh I feel so stupid trying to figure this out!


cos(ax+b)dx=sin(ax+b)a+k\displaystyle \int \cos (ax+b) \, dx = \frac{\sin (ax+b)}{a}+k
Reply 6
For question 2, another way of writing that, which i find clearer would be

1/ (x+1)^1/2 x dx

then its been put into the form of any other integral you are used to?
Hope that makes sense, i don't know how to do the integral signs etc :P
Reply 7
Original post by TheHaylio
F

1/ (x+1)^1/2 x dx



Where does this x come from
Reply 8
Original post by TenOfThem
Where does this x come from


meant to be a multiplied sign sorry :biggrin:
Reply 9
Original post by TenOfThem
Can you do cos(3x)dx\int \cos (3x) dx as the method is the same

Would that be 1/3sin3x+c?
Sorry, I obviously have no idea how to insert equations here either.

I know the chain rule for standard integrals, but I think the fraction is just throwing me a bit.

cos (ax+b) dx = 1/a sin (ax+b) + x

so in my problem, would a = πx? or would a = πx/2? or am I still totally wrong?

Thanks for this btw!
Reply 10
Original post by TheHaylio
For question 2, another way of writing that, which i find clearer would be

1/ (x+1)^1/2 x dx

then its been put into the form of any other integral you are used to?
Hope that makes sense, i don't know how to do the integral signs etc :P

Yes that's exactly what I thought it meant, but I wasn't sure if it was a totally different problem or just another way of writing it. So let me get this right, even if the dx is a numerator to what I'm trying to integrate, it still means I'm just integrating it with respect to x, yeah?

If that's right, then you've honestly just made my day hahaha
Original post by angelooo
Would that be 1/3sin3x+c?



Yes, essentially you just divide by the constant and in your question the constant will be π2\frac{\pi}{2}
Original post by angelooo
Yes that's exactly what I thought it meant, but I wasn't sure if it was a totally different problem or just another way of writing it. So let me get this right, even if the dx is a numerator to what I'm trying to integrate, it still means I'm just integrating it with respect to x, yeah?

If that's right, then you've honestly just made my day hahaha


Yes

dxf(x)=1f(x)dx\displaystyle \int \dfrac{dx}{f(x)} = \displaystyle \int \dfrac{1}{f(x)} dx
Reply 13
Original post by angelooo
Yes that's exactly what I thought it meant, but I wasn't sure if it was a totally different problem or just another way of writing it. So let me get this right, even if the dx is a numerator to what I'm trying to integrate, it still means I'm just integrating it with respect to x, yeah?

If that's right, then you've honestly just made my day hahaha


Yep :smile:
hhaha, good!
Original post by TheHaylio
meant to be a multiplied sign sorry :biggrin:


http://www.numberempire.com/texequationeditor/equationeditor.php

use that, it prevents ambiguous equations and saves time having to learning how to use latex

just copy and paste the expression
Reply 15
I wish I could give all a big cuddle or something to show my gratitude! I also wish I'd come here when I was first struggling for help because it would've saved a massive headache hahaha. Thanks so much everyone, you're all stars!
Reply 16
Original post by TenOfThem
Yes

dxf(x)=1f(x)dx\displaystyle \int \dfrac{dx}{f(x)} = \displaystyle \int \dfrac{1}{f(x)} dx


Looks so much better with the symbals :P
Reply 17
Original post by upthegunners
http://www.numberempire.com/texequationeditor/equationeditor.php

use that, it prevents ambiguous equations and saves time having to learning how to use latex

just copy and paste the expression


Thanks!
Reply 18
Original post by angelooo
I wish I could give all a big cuddle or something to show my gratitude! I also wish I'd come here when I was first struggling for help because it would've saved a massive headache hahaha. Thanks so much everyone, you're all stars!


Haha! Thats okay, i always end up asking for help here- it's good to be able to actually give some help back for once!
Original post by angelooo
I wish I could give all a big cuddle or something to show my gratitude! I also wish I'd come here when I was first struggling for help because it would've saved a massive headache hahaha. Thanks so much everyone, you're all stars!


NP

:hugs:

Quick Reply

Latest