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Math Expert
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Re: M28-13 [#permalink]
Expert Reply
Viktorijakm wrote:
I think this question is poor.
it is 29 in the question ,but factoring shows 25!!!


You are wrong.

Did you try to expand (x^2 - 25)(x^2 - 4) = 0? You'll get x^4 - 29x^2 + 100 = 0, which is the same as x^4 = 29x^2 - 100.
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Re: M28-13 [#permalink]
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I think this is a high-quality question and I agree with explanation.
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Re: M28-13 [#permalink]
Viktorijakm wrote:
I think this question is poor.
it is 29 in the question ,but factoring shows 25!!!


The factoring is correct though, as you are looking for numbers which add to -29 and multiply to 100 respectively.

I think the question is of high quality and similar to stuff I have seen on the GMAC prep tests.
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Re: M28-13 [#permalink]
I think this is a high-quality question.
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Re: M28-13 [#permalink]
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Great question

An alternative approach:

\(x^4 - 29x^2 + 100 = 0\)

Create a variable \( y = x^2 \)
\(x^4 - 29x^2 + 100 \)
\(y^2-29y^2+100 = 0\)

y = 25 or y = 4

Substitute the values of y in the equation \( y = x^2 \)
\(x = y^2\)

Find X:
If y = 25 then x = 5 or x = -5
If y = 4 then x = 2 or x = -2
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Re: M28-13 [#permalink]
Expert Reply
I have edited the question and the solution by adding more details to enhance its clarity. I hope it is now easier to understand.
GMAT Club Bot
Re: M28-13 [#permalink]
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