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abhichatur
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Is the presence of imaginary numbers completely neglected on the gmat? 30 Apr 2020, 06:00
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I was doing a DS question where I got 5^x=root(625) so I thought there are two answers and hence insufficient. However the solution says that 5^x can never be negative and hence we must neglect that. I understand this fact but again there are numbers which can get a 5 power negative. Im just confused on such questions as to when to take a +/- approach and when not. Please help me.
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Is the presence of imaginary numbers completely neglected on the gmat? 30 Apr 2020, 07:35
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Hi abhichatur
Can you post the whole question for better understanding?
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Is the presence of imaginary numbers completely neglected on the gmat? 30 Apr 2020, 07:53
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as per your question
5^x = 625
so x = 4
it is not a gmat concept
under roots of positive numbers are not imaginary
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Is the presence of imaginary numbers completely neglected on the gmat? 30 Apr 2020, 08:28
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abhichatur
I was doing a DS question where I got 5^x=root(625) so I thought there are two answers and hence insufficient. However the solution says that 5^x can never be negative and hence we must neglect that. I understand this fact but again there are numbers which can get a 5 power negative. Im just confused on such questions as to when to take a +/- approach and when not. Please help me.
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Going by headline of your post yes imaginary numbers are not tested in GMAT. Reading the content of your post, I could not relate anything to imaginary numbers' concept. May be you would like to elaborate.
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Is the presence of imaginary numbers completely neglected on the gmat? Updated on: 03 May 2020, 13:49
Originally posted by freedom128 on 30 Apr 2020, 10:16.
Last edited by freedom128 on 03 May 2020, 13:49, edited 1 time in total.
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5^(4i)=625? It is clear that no imaginary number concept and calculation is needed. Perhaps, post the entire question so that we can work it together.

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Is the presence of imaginary numbers completely neglected on the gmat? 30 Apr 2020, 15:12
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abhichatur
I was doing a DS question where I got 5^x=root(625) so I thought there are two answers and hence insufficient. However the solution says that 5^x can never be negative and hence we must neglect that. I understand this fact but again there are numbers which can get a 5 power negative. Im just confused on such questions as to when to take a +/- approach and when not. Please help me.
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Hi abhichatur

x = 4> 0 is a solution since \(5^4 = 625\)
x = -4 is not a solution since \(5^{-4} = 1/625\)
What is the confusion?
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Is the presence of imaginary numbers completely neglected on the gmat? 03 May 2020, 06:40
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abhichatur
I was doing a DS question where I got 5^x=root(625) so I thought there are two answers and hence insufficient. However the solution says that 5^x can never be negative and hence we must neglect that. I understand this fact but again there are numbers which can get a 5 power negative. Im just confused on such questions as to when to take a +/- approach and when not. Please help me.
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If your question read:

\(\\
5^x = \sqrt{625}\\
\)

then the right side, √625, is equal to 25, and never to -25, because the "√" symbol is defined in math to mean "the non-negative square root". So your equation simplifies to

\(\\
5^x = 25\\
\)

It is true that this equation has infinitely many solutions if x is allowed to be a complex number (that follows immediately from Euler's famous formula) but the instructions on the GMAT tell you that every number on the test is a real number. So x cannot be a complex number, and in that case this equation has only one solution, x = 2 (I'm not sure why every post above says the answer is 4, which is not right).

Complex numbers are never tested on the GMAT, so it's best to try to forget anything you've learned about them if you're preparing for the test.
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Is the presence of imaginary numbers completely neglected on the gmat? 03 Oct 2024, 23:48
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Sorry guys, just saw this post I made years ago (and subsequently dropped studying and the attempt all together). Thanks for all your help on the post. Yes, 5^x being root 625 has nothing to do with imaginary numbers and so does the test!
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