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Problem Solving — algebra and arithmetic (GMAT Focus Edition)
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Source: — Quantitative Reasoning |
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by Tani » Sun Feb 20, 2011 8:33 am
Let f(x) = y

y = (x+1)/(x+2)

solve for x

y(x+2) = (X+1)
xy + 2y = x + 1
xy - x = 1 - 2y
x(y-1) = 1-2y
x = (1-2y)/(y-1)

now switch x and y

y = (1-2x)/(x-1)
f(x) = (1-2x)/(x-1)
Tani Wolff
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by gettowar » Sun Feb 20, 2011 4:44 pm
Tani,
It should be y=(x+1)(x-2), not y=(x+1)(x-2). The steps are the same though.
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by marmar29 » Sun Feb 20, 2011 11:58 pm
Tani Wolff - Kaplan wrote:Let f(x) = y

y = (x+1)/(x+2)

solve for x

y(x+2) = (X+1)
xy + 2y = x + 1
xy - x = 1 - 2y
x(y-1) = 1-2y
x = (1-2y)/(y-1)

now switch x and y

y = (1-2x)/(x-1)
f(x) = (1-2x)/(x-1)


thanks alooot tani but with me i got 1+2x / x-1 the same as the model answer at the back & u giot it -2x !!
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by Tani » Mon Feb 21, 2011 6:13 pm
Sorry - I copied the problem down wrong - started with (x+2) instead of (x-2) - trying to type math problems sometimes messes me up.
Tani Wolff
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