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radical sign question

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Junior | Next Rank: 30 Posts
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radical sign question

by beter2jump » Wed Jul 22, 2009 7:46 am
hi,

i have trouble solving this. any help will be appreciated :

3radical sign (x+y) = c^8

what is x+y ?[/quote]
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by truplayer256 » Wed Jul 22, 2009 10:22 am
3*sqrt(x+y)=c^8

sqrt(x+y)=c^8/3

Square both sides to get:

x+y=(c^8/3)^(2)=c^16/9
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ans

by beter2jump » Wed Jul 22, 2009 10:59 am
the ans to this question was

x+y = C^18
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by truplayer256 » Thu Jul 23, 2009 9:45 am
I'm pretty sure that the answer is not x+y=c^18 unless you typed the question incorrectly. May I know the source of this question?
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question

by beter2jump » Thu Jul 23, 2009 9:58 am
as i cant type the radical sign the qn seems awkward.

in fact its not 3*sqrt(x+y), the three is on the left of sqrt on the sqrt sign.
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by truplayer256 » Thu Jul 23, 2009 11:15 am
as i cant type the radical sign the qn seems awkward.

in fact its not 3*sqrt(x+y), the three is on the left of sqrt on the sqrt sign.
Oh, okay. This makes a lot more sense now :)

So the question is really:

cubic root of (x+y)= c^8

All we do here is take the cube of both sides:

x+y=(c^8)^(3)=c^24... It still doesn't match the OA. Why's this?
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by Stuart@KaplanGMAT » Thu Jul 23, 2009 1:08 pm
truplayer256 wrote:
as i cant type the radical sign the qn seems awkward.

in fact its not 3*sqrt(x+y), the three is on the left of sqrt on the sqrt sign.
Oh, okay. This makes a lot more sense now :)

So the question is really:

cubic root of (x+y)= c^8

All we do here is take the cube of both sides:

x+y=(c^8)^(3)=c^24... It still doesn't match the OA. Why's this?
I agree - are you sure that the original question didn't read c^6 instead of c^8?
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Junior | Next Rank: 30 Posts
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right

by beter2jump » Thu Jul 23, 2009 1:48 pm
I don't know as i noted this problem during a review quickly ...

My confusion is cleared though, as i was not sure how to remove cube root from one side , which the ans have demonstrated ...

thanks for all.
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