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# Maths HELP - C4 Integration watch

1. (Original post by creativebuzz)
Oh okay! But when I plug the limits into my calculator I get 0 for 1 and an error for -1
Remember that when you integrate you will get 0.5ln|2x-1| so remember the modulus signs
2. (Original post by TenOfThem)
The answer I would expect would be 0.5(ln1 - ln3) = -0.5ln3
...
3. (Original post by TeeEm)
...
It wouldn't be asked in an exam (hopefully)
4. (Original post by TenOfThem)
It wouldn't be asked in an exam (hopefully)
I hope not.

(an answer can be obtained of course but definitely wrong)
5. (Original post by TenOfThem)
Remember that when you integrate you will get 0.5ln|2x-1| so remember the modulus signs
Does that mean that instead of getting 0.5ln|-3| I would get 0.5ln|3|?
6. (Original post by TeeEm)
I hope not.

(an answer can be obtained of course but definitely wrong)
Sure

But the point of the exercise is to test a limited understanding ... That is how text books are produced

7. (Original post by creativebuzz)
Does that mean that instead of getting 0.5ln|-3| I would get 0.5ln|3|?
Yes
8. (Original post by TenOfThem)
Yes
Thanks!

As for the last one, I did the fourth root got
I = 2sinxcos
= sin2x

therefore it's =1/2cos2x + c

Where did I go wrong? :/
9. (Original post by creativebuzz)
Thanks!

As for the last one, I did the fourth root got
I = 2sinxcos
= sin2x

therefore it's =1/2cos2x + c

Where did I go wrong? :/
Taking the 4th root was only so you could find the sin2x

So you need to integrate (sin2x)^4
10. [QUOTE=TenOfThem;53124173]Taking the 4th root was only so you could find the sin2x

Woo, I got the right answers! Thanks

As for K, I think I've got in a muddle but this is my working out so far:

Attached Images

11. [QUOTE=creativebuzz;53126211]
(Original post by TenOfThem)
Taking the 4th root was only so you could find the sin2x

Woo, I got the right answers! Thanks

As for K, I think I've got in a muddle but this is my working out so far:

You do not want a mix of x and 2x

You can always integrate cosx sin^nx by inverse chain rule

So change your cos^3x into cocs^2xcosx and then change the cos^2x into 1-sin^2x

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Updated: January 22, 2015
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