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C2 soloman paper B. integration with an infinate limity

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Reply 20
Original post by thefatone
so what about OP's question?

i integrated and got 4x324x^ {\dfrac -{3}{2}}

then i put values in and got

[0]-[1.414]
so is -1.414 correct as an answer?


You've messed up your LaTeX\LaTeX. The function is positive everywhere in the domain of integration; does a negative answer really make sense? You mean 2\sqrt{2}, not 1.414.
Original post by Zacken
You've messed up your LaTeX\LaTeX. The function is positive everywhere in the domain of integration; does a negative answer really make sense? You mean 2\sqrt{2}, not 1.414.


better? i changed it

oh ... i just used my calculator but yes 2 \sqrt 2

so does that mean the area i got is below the x-axis?
Reply 22
Original post by thefatone
better? i changed it

oh ... i just used my calculator but yes 2 \sqrt 2

so does that mean the area i got is below the x-axis?


No, it means you integrated wrong.
Original post by Zacken
No, it means you integrated wrong.


aww s**t let's try again

6x52=6x52\dfrac{6}{x^ \frac {5}{2}} = 6x^{-\frac {5}{2}}

so integrating

6x3232\displaystyle \frac{6x^{-\frac{3}{2}}}{-\frac{3}{2}}

4x32 -4x^{-\frac{3}{2}}

subbing infinity gives 0

subbing 2 in gives (2) -\left( \sqrt 2\right)

[0][2][0]-[-\sqrt 2]

so i get positive 2\sqrt 2????
(edited 8 years ago)
Reply 24
Original post by thefatone
...


Where'd the negative in the denominator go?
Original post by Zacken
Where'd the negative in the denominator go?


oh.... lemme change that
Reply 26
Original post by thefatone
oh.... lemme change that


Okay, it's fine now. Now do your limits and remember the negative signs.
Original post by Zacken
Okay, it's fine now. Now do your limits and remember the negative signs.


all better? (editied)
Reply 28
Original post by thefatone
all better? (editied)


Yes.

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