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If (2x + 1)^2 = 100, then which one of the following COULD equal x ?

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If (2x + 1)^2 = 100, then which one of the following COULD equal x ? [#permalink]

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New post 04 Mar 2017, 00:47
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If (2x + 1)^2 = 100, then which one of the following COULD equal x ?

(A) –11/2

(B) –9/2

(C) 11/2

(D) 13/2

(E) 17/2
Spoiler: OA
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Re: If (2x + 1)^2 = 100, then which one of the following COULD equal x ? [#permalink]

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New post 04 Mar 2017, 05:23
(2x + 1)^2 = 100
=>2x + 1 = +/- (10)
=>2x = 9. Or. => 2x = -11
Therefore, x = 9/2 or x = -11/2

Answer A.
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Re: If (2x + 1)^2 = 100, then which one of the following COULD equal x ? [#permalink]

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New post 04 Mar 2017, 07:45
(2x+1)^2=100

Either 2x+1=10 => 2x=9 => x=9/2
Or 2x+1=-10 => 2x=-11 => x=-11/2

Answer A
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If (2x + 1)^2 = 100, then which one of the following COULD equal x ? [#permalink]

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New post 04 Mar 2017, 08:06
vikasp99 wrote:
If (2x + 1)^2 = 100, then which one of the following COULD equal x ?

(A) –11/2

(B) –9/2

(C) 11/2

(D) 13/2

(E) 17/2


There are 2 possible values of 2x + 1

\(2x + 1 = 10\) , so \(x = \frac{9}{2}\)
\(2x + 1 = -10\) so \(x = \frac{-11}{2}\)

Thus, answer will be (A) \(\frac{-11}{2}\)
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Re: If (2x + 1)^2 = 100, then which one of the following COULD equal x ? [#permalink]

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New post 06 Mar 2017, 12:44
1
Hi vikasp99,

This question asks which of the 5 answers COULD be the solution to the given equation. When a question 'hints' that there's more than one possible solution, it's likely that the "obvious" answer will not be the one that's included in the answers.

There are two numbers - that when squared - equal 100: +10 and -10.

Thus, if we were asked for BOTH solutions, then we would have to set up 2 equations:

2X + 1 = +10
2X + 1 = -10

However, it's likely that the second option will be the one that we'll need (since it's the less-obvious solution)...

2X + 1 = -10
2X = -11
X = -11/2

Final Answer:
Spoiler: ::
A


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Re: If (2x + 1)^2 = 100, then which one of the following COULD equal x ?   [#permalink] 06 Mar 2017, 12:44
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