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GMATH practice question (Quant Class 13)

If \(a\) and \(b\) are constants such that \(\,\,{{ax} \over {{x^2} - 1}} + {b \over {x - 1}} = {{2x - 1} \over {{x^2} - 1}}\,\,\) for every \(x > 1\), what is the value of \(a - b\) ?

(A) -2
(B) -1
(C) 0
(D) 2
(E) 4

Source: https://www.gmath.net

ax + b x + b = 2x -1 , for x > 1

a - b = ?

(a+b)x + b = 2x - 1

b = -1, then a+b = 2
a = 3

Now a - b = 3 +1 = 4

E


Hi KanishkM :)

How did you end with (a+b)x + b = 2x - 1?
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GMATH practice question (Quant Class 13)

If \(a\) and \(b\) are constants such that \(\,\,{{ax} \over {{x^2} - 1}} + {b \over {x - 1}} = {{2x - 1} \over {{x^2} - 1}}\,\,\) for every \(x > 1\), what is the value of \(a - b\) ?

(A) -2
(B) -1
(C) 0
(D) 2
(E) 4

Source: https://www.gmath.net

ax + b x + b = 2x -1 , for x > 1

a - b = ?

(a+b)x + b = 2x - 1

b = -1, then a+b = 2
a = 3

Now a - b = 3 +1 = 4

E


Hi KanishkM :)

How did you end with (a+b)x + b = 2x - 1?

Hey jfranciscocuencag

Just expand x^2-1 to x+1 x-1

Cross out the common terms from both LHS and RHS

After that you can take LCM and easily solve the question.

Posted from my mobile device
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If \(a\) and \(b\) are constants such that \(\,\,{{ax} \over {{x^2} - 1}} + {b \over {x - 1}} = {{2x - 1} \over {{x^2} - 1}}\,\,\) for every \(x > 1\), what is the value of \(a - b\) ?

\(\frac{ax}{x^2 - 1} + \frac{b}{x-1} = \frac{2x-1}{x^2-1}\)
\(\frac{ax}{x^2 - 1} + \frac{b(x+1)}{x^2-1} = \frac{2x-1}{x^2-1}\)
\(ax + bx + b = 2x - 1\)

a + b = 2
b = -1
a = 3
a - b = 3 - (-1) = 4

IMO E
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