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 Q51  V47
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Re: If |x^2 - x + 1| = 2x -1, then what is the sum of all possible values [#permalink]
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Bunuel wrote:
If \(|x^2-x+1|=2x-1\), then what is the sum of all possible values of x ?


You might notice if 2x - 1 equals the absolute value of something, then 2x - 1 must be at least zero, and x must be at least 1/2, so certainly x must be positive. But on the left side, we're taking the absolute value of x^2 - x + 1, which is equal to x^2 - 2x + 1 + x = (x - 1)^2 + x. So we're taking the absolute value of a square, which must be zero or greater, plus some positive value x, and the expression inside the absolute value must be positive (there are several other ways to see that, some simpler if you use slightly more advanced math). So the absolute value isn't doing anything here, because we're taking the absolute value of something that must already be positive, and we can just ignore the absolute value and solve the equation

x^2 - x + 1 = 2x - 1
x^2 - 3x + 2 = 0
(x - 2)(x - 1) = 0

and x = 2 or x = 1, and the sum of the solutions is 3.
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Re: If |x^2 - x + 1| = 2x -1, then what is the sum of all possible values [#permalink]
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Bunuel wrote:
If \(|x^2-x+1|=2x-1\), then what is the sum of all possible values of x ?

A. 0

B. 1

C. 2

D. 3

E. 4


The right side tells us \(2x - 1 > 0\) and \(x > \frac{1}{2}\).

Also note the left side must be positive no matter what real x you plug in. We can see that from the determinant \(b^2 - 4ac = 1 - 4 = -3 < 0\) or \(x^2 - x + 1 = (x - 1)^2 + x > 0\) since x > 0.

Therefore \(x^2 - x + 1\) is always positive and we yield \(x^2 - x + 1 =2x - 1\), which is \(x^2 - 3x + 2 = 0\)

\(x = 1\) or \(x = 2\), we may plug in to double-check but they both satisfy x > 0.5 so we accept both.

Ans: D
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Re: If |x^2 - x + 1| = 2x -1, then what is the sum of all possible values [#permalink]
Bunuel wrote:
If \(|x^2-x+1|=2x-1\), then what is the sum of all possible values of x ?

A. 0

B. 1

C. 2

D. 3

E. 4

When the eqn is positive through simplification we get
=>x^2 -3x +2 =0
=> x=2 ,1

When the eqn is negative
=>x^2 +x =0
=>x=0 ,x=-1

HOwever when resubstitute and check for the answer we get
x=2,1,0

Therefore IMO D
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Re: If |x^2 - x + 1| = 2x -1, then what is the sum of all possible values [#permalink]
Since 2x-1 >= 0, x > 1/2 ....................inferred from the question stem itself.

1. When |x^2 - x + 1| > 0
|x^2 - x + 1| = 2x -1
Solving this we get x = 2 or x = 1 ...........Possible values, Sum = 3

2. When |x^2 - x + 1| < 0
- |x^2 - x + 1| = 2x -1
Solving this we get x = 0 or x = -1. But from our inference earlier, x > 1/2.

Hence sum of all possible values of x = 2+1 =3
IMHO Answer D
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Re: If |x^2 - x + 1| = 2x -1, then what is the sum of all possible values [#permalink]
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Bunuel wrote:
If \(|x^2-x+1|=2x-1\), then what is the sum of all possible values of x ?

A. 0

B. 1

C. 2

D. 3

E. 4





This question is a part of Are You Up For the Challenge: 700 Level Questions collection.
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Re: If |x^2 - x + 1| = 2x -1, then what is the sum of all possible values [#permalink]
Bunuel wrote:
If \(|x^2-x+1|=2x-1\), then what is the sum of all possible values of x ?

A. 0

B. 1

C. 2

D. 3

E. 4


M37-03


There are 2 possible cases:

Case 1, \(x^2-x+1\) is positive,

Equation becomes,
\(x^2-x+1=2x-1\)
=> \(x^2-3x+2=0\)
=> x = 2,1

Case 2, \(x^2-x+1\) is negative

Equation becomes
\(x^2-x+1=-(2x-1)\)
=> x=0,-1 Both doesn't satisfy the original equation

Since, only x=2 and x=1 satisfy the equation \(|x^2-x+1|=2x-1\)
Therefore, the sum of all possible values of x is 2+1 = 3

D is Correct
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Re: If |x^2 - x + 1| = 2x -1, then what is the sum of all possible values [#permalink]
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Re: If |x^2 - x + 1| = 2x -1, then what is the sum of all possible values [#permalink]
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