You are Here: Home >< A-levels

# INTEGRATION- where did I go wrong? watch

1. Substitution question

(Q4 of Jan2013 edexcel C4)

Anyway

y= x/(1+ sqroot x)

use u= 1 + sqr x

soo what I did:

rearraged some to get

sqr x= u - 1
x= (u - 1)^2

and I got dx= 2(u-1)

so

integral of (u-1)^2/1+ (u-1) * 2(u-1) du

cancelled the u-1 to get

integral of 2(u-1)^2 du

took the 2 out

integrated (u -1)^2 and I got (u-1)^3 /(3)
so

2/3 (1 + sqr x)^3 + c

where did I go wrong
2. You can't cancel the (u-1) because you have 1+ (u-1) on the denominator
3. (Original post by Student403)
You can't cancel the (u-1) because you have 1+ (u-1) on the denominator

Posted from TSR Mobile
4. (Original post by Student403)
You can't cancel the (u-1) because you have 1+ (u-1) on the denominator
Oh lmao

Thanks
5. (Original post by Dinaa)
Oh lmao

Thanks
Sure
6. (Original post by Student403)
You can't cancel the (u-1) because you have 1+ (u-1) on the denominator

Question

Is my dx ok?

I know I could find du/dx, but instead I found dx/du and multiplied everything by du.
7. (Original post by Dinaa)
Question

Is my dx ok?

I know I could find du/dx, but instead I found dx/du and multiplied everything by du.
Yeah it's fine. I did the same and got 2(u-1)
8. You tried to integrate e^x and everyone knows e^x doesn't like to integrate.
9. (Original post by Awesome Genius)
You tried to integrate e^x and everyone knows e^x doesn't like to integrate.

10. (Original post by Student403)

So there's this function party going on and all of the hippest functions are there having a good time. Cos(x) is getting down and dirty with ln(x), 10^x is making the moves on the (x - 2)^2 twins and even x! dragged himself out for a good time.Unfortunately, one little function just wasn't having her night. e^x was sitting in a chair in the corner, tears dripping down exponentially. Sin(x) catches her out of the corner of his eye and decides to cheer her up. "Come on e^x! There's no reason to sit all on your lonesome crying. Get out into the crowd and have some fun. You know, INTEGRATE a little bit."e^x looks at Sin(x) with the saddest eyes and exclaims, "But it won't make any difference!"
11. (Original post by Awesome Genius)
So there's this function party going on and all of the hippest functions are there having a good time. Cos(x) is getting down and dirty with ln(x), 10^x is making the moves on the (x - 2)^2 twins and even x! dragged himself out for a good time.Unfortunately, one little function just wasn't having her night. e^x was sitting in a chair in the corner, tears dripping down exponentially. Sin(x) catches her out of the corner of his eye and decides to cheer her up. "Come on e^x! There's no reason to sit all on your lonesome crying. Get out into the crowd and have some fun. You know, INTEGRATE a little bit."e^x looks at Sin(x) with the saddest eyes and exclaims, "But it won't make any difference!"
12. (Original post by Awesome Genius)
You tried to integrate e^x and everyone knows e^x doesn't like to integrate.
no not really, e^x integrates to e^x

its lnx that doesn't like integrating
Spoiler:
Show
well it does if you use integration by parts ( *1) and make u lnx.. but shh

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: March 15, 2016
Today on TSR

### A-Level OCR Biology Unofficial Markscheme

Find out how you've done here

### 1,801

students online now

Exam discussions

Poll

## All the essentials

### Student life: what to expect

What it's really like going to uni

### Essay expert

Learn to write like a pro with our ultimate essay guide.

### Create a study plan

Get your head around what you need to do and when with the study planner tool.

### Resources by subject

Everything from mind maps to class notes.

### Study tips from A* students

Students who got top grades in their A-levels share their secrets