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OG 11, DS #145, Am i missing something?

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OG 11, DS #145, Am i missing something?

by jaheer » Sat Feb 17, 2007 12:36 am
Is (1/p)>r/(r^2+2)

1) p=r
2) r>0

from the above equation i simplified the question into

Is (r^2+2)>pr ( Can i do this) If i can then

when i plug in the 1st choice I have

r^2+2 >r^2 ( which will always be true). So, accordingly A should be the correct answer. Please correct me.
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by banona » Sat Feb 17, 2007 5:20 am
Hi jaheer,

For all inequalities, be sure to know the sign of each number before to simplify any inequality;
What you did to reach the following expresion (r^2+2)>pr from 1/P > r/(r^2+2) is that you have multiplied by P and then by ( r^2+2) EACH side of the inequality,
you can not do that untless you know the sign of P,
Therfore, 1 and 2 together give suffisants conditions to answer the question,

If you are still not confident with, consider 1 that tell p=r without any information about the sign; than we can pick 1 and -1 as values of p and r;
in the first case p=r=1 ; 1/r =1 > 1/( 2+2) ( it's fine)
in the second case,p=r=-1; 1/r = -1 and ( r/( r^2+2) )= -1/3 ( it's not much fine here)

I hope I am right and clear[/b]
I appologize for my Frenchy-English.
I am working on it.
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by jaheer » Sat Feb 17, 2007 6:22 am
Aha! Thanks. Got it.

Your "Frenchy English" is not bad at all ( except for few French Spellings :-)).

Good Luck.
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og ds 145

by simba12123 » Fri Oct 24, 2008 6:41 am
wonderful explanation. I am a bit conufesed on one think.. I made the same mistake of simplifying without paying respect to the rules..

What is the takeaway here. WHen can we simplify?

The reason i ask is there is no negative sign in from of p or and r^2 is obviously positive. THerefore arent all pos and neg signs accounted for?
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Senior | Next Rank: 100 Posts
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og ds 145

by simba12123 » Fri Oct 24, 2008 6:41 am
wonderful explanation. I am a bit conufesed on one think.. I made the same mistake of simplifying without paying respect to the rules..

What is the takeaway here. WHen can we simplify?

The reason i ask is there is no negative sign in from of p or and r^2 is obviously positive. THerefore arent all pos and neg signs accounted for?
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by jsl » Fri Oct 24, 2008 7:14 am
note that on this solution, for the denominator on the RHS (r^2 + 2)... you can multiply this to the top of the LHS. You can do this because r^2 is ALWAYS positive and therefre (r^2 + 2) is always a positive answer.

Is the OA C?
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by rohangupta83 » Fri Oct 24, 2008 7:21 am
has to be (C)
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