If r@s = rs + r + s, then for what value of s is r@s equal : PS Archive
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# If r@s = rs + r + s, then for what value of s is r@s equal

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If r@s = rs + r + s, then for what value of s is r@s equal [#permalink]

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30 May 2007, 21:07
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15. If r@s = rs + r + s, then for what value of s is r@s equal to r for all values of r?
(A) –1
(B) 0
(C) 1
(D) 1 / (r+1)
(E) r

i have no idea how to set this up
SVP
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30 May 2007, 22:38
(B) for me

we have:
o r@s = rs + r + s
and
o r@s = r

Then,
rs + r + s = r
<=> s*(r+1) = 0

So, it's s = 0 that gives us r@s = r as 0 * (r+1) = 0 for any r.
Manager
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Re: PS # 15 functions [#permalink]

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30 May 2007, 22:54
(B)

rs + r + s = r (for all value of r)
rs + s = 0
s*(r+1) = 0
s = 0
Re: PS # 15 functions   [#permalink] 30 May 2007, 22:54
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