An algebra problem by A Former Brilliant Member

Algebra Level 1

Solve:

x x 2 1 1 x 2 1 + 2 x + 1 = 0 \large \dfrac{x}{x^2-1}-\dfrac{1}{x^2-1}+\dfrac{2}{x+1}=0

1 0 The equation has no root. 3

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4 solutions

x x 2 1 1 x 2 1 + 2 x + 1 = 0 \large \dfrac{x}{x^2-1}-\dfrac{1}{x^2-1}+\dfrac{2}{x+1}=0

The L C D LCD is x 2 1 x^2-1 . So

x 1 + 2 ( x 1 ) x 2 1 = 0 \large \dfrac{x-1+2(x-1)}{x^2-1}=0 \implies x 1 + 2 x 2 = 0 \large x-1+2x-2=0 \implies 3 x = 3 \large 3x=3 \implies x = 1 \large x=1

Since x = 1 x=1 makes x 2 1 = 0 x^2-1=0 in the given denominators, x = 1 x=1 cannot be accepted as a root because division by z e r o zero is not admissible. Hence, 1 1 is an extraneous root and the given equation has n o r o o t no~root .

Jaydee Lucero
Jun 27, 2017

Note that x x 2 1 1 x 2 1 + 2 x + 1 = x 1 x 2 1 + 2 x + 1 = x 1 ( x 1 ) ( x + 1 ) + 2 x + 1 = 1 x + 1 + 2 x + 1 = 3 x + 1 \frac{x}{x^2 - 1} -\frac{1}{x^2 - 1}+\frac{2}{x+1} = \frac{x-1}{x^2 - 1}+\frac{2}{x+1}=\frac{x-1}{(x-1)(x+1)}+\frac{2}{x+1}=\frac{1}{x+1}+\frac{2}{x+1}=\frac{3}{x+1} which cannot be equal to 0 0 for all real numbers x x . Therefore, the equation has no root .

I have another way.

0 = x x 2 1 1 x 2 1 + 2 x + 1 0 = x 1 x 2 1 + 2 x + 1 0 = x 1 ( x + 1 ) ( x 1 ) + 2 x + 1 0 = x 1 + 2 ( x 1 ) ( x + 1 ) ( x 1 ) 0 = x 1 + 2 x 2 ( x + 1 ) ( x 1 ) 0 = 3 x 3 ( x + 1 ) ( x 1 ) 0 = 3 ( x 1 ) ( x + 1 ) ( x 1 ) 0 = 3 x + 1 ( x + 1 ) 2 0 = 3 ( x + 1 ) 0 = x + 1 1 = x 0=\frac { x }{ { x }^{ 2 }-1 } -\frac { 1 }{ { x }^{ 2 }-1 } +\frac { 2 }{ x+1 } \\ 0=\frac { x-1 }{ { x }^{ 2 }-1 } +\frac { 2 }{ x+1 } \\ 0=\frac { x-1 }{ (x+1)(x-1) } +\frac { 2 }{ x+1 } \\ 0=\frac { x-1+2(x-1) }{ (x+1)(x-1) } \\ 0=\frac { x-1+2x-2 }{ (x+1)(x-1) } \\ 0=\frac { 3x-3 }{ (x+1)(x-1) } \\ 0=\frac { 3(x-1) }{ (x+1)(x-1) } \\ 0=\frac { 3 }{ x+1 } \cdot { (x+1) }^{ 2 }\\ 0=3(x+1)\\ 0=x+1\\ -1=x\\

If x = 1 x = -1 then how does 0 = 1 ( 1 ) 2 1 1 ( 1 ) 2 1 + 2 1 + 1 = 1 0 1 0 + 2 0 0 = \dfrac{-1}{(-1)^2-1}-\dfrac{1}{(-1)^2-1}+\dfrac{2}{-1+1} = \dfrac{-1}{0}-\dfrac{1}{0}+\dfrac{2}{0} lends a value as it is dividing by 0 0 ?

Vu Vincent - 3 years, 9 months ago
Angad Narula
Jul 1, 2017

Can anyone please tell me how can I make my own questions and post them on brilliant??

If you see the left side, there is the word Community, click it.. Then click post...

A Former Brilliant Member - 3 years, 11 months ago

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