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# practice problem

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Intern
Joined: 14 Jul 2003
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12 Aug 2003, 12:05
this is an actual practice problem i came across

if x = -1, what is -x^2?

is it 1 or -1?

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Intern
Joined: 01 Aug 2003
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12 Aug 2003, 12:11
goldsjo wrote:
this is an actual practice problem i came across

if x = -1, what is -x^2?

is it 1 or -1?

Any number (positive or negative) raised to an even power is positive.

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Manager
Joined: 11 Mar 2003
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13 Aug 2003, 17:31
Shouldn't this be -1? because x = -1

so -X^2 = -(-1)^2 = -1

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Intern
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14 Aug 2003, 05:57
goldsjo wrote:
this is an actual practice problem i came across

if x = -1, what is -x^2?

is it 1 or -1?

Ans: -1

-(-1)^2= -1

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Intern
Joined: 04 Aug 2003
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14 Aug 2003, 09:50
andy_taiwan wrote:
goldsjo wrote:
this is an actual practice problem i came across

if x = -1, what is -x^2?

is it 1 or -1?

Ans: -1

-(-1)^2= -1

I'm seeing two different answers here. Can someone confirm if its -1 or 1?
If you follow the logic that a negative x a negative = positive you get one. But if you follow the Order of operations, exponents come first and -*1 =
-1

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Manager
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14 Aug 2003, 10:40
Follow the order of operations and get -1. As it is written that is the correct answer.

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Intern
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14 Aug 2003, 11:43
Oops....I stand corrected. I fell for the trap. Sorry if I confused you. Everyone is right, the answer is -1. My apologies.

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Manager
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15 Aug 2003, 07:05
If x = -1 then -x^2=1 and -(x^2)=-1 !!!

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GMAT Instructor
Joined: 07 Jul 2003
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Schools: Haas, MFE; Anderson, MBA; USC, MSEE

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15 Aug 2003, 07:54
goldsjo wrote:
this is an actual practice problem i came across

if x = -1, what is -x^2?

is it 1 or -1?

The interpretation of -x^2 as -(x^2) is correct according to agreements made by international math authorities. It is more convincing when it is typeset properly with the exponent as a superset number. Another way of getting this right is to substitute "(-1)*" for the "-".
Hence -x^2 = (-1)*x^2 and it is clearly (-1)*(x^2).

What makes this a somewhat confusing question is that: 1) most of the popular lists of algebraic precedence rules (e.g., PEMDAS) ignore the unary functions "+" and "-" when it should be properly placed below Exponentiation and above Multiplication/Division; and 2) one of the most widely used programs, Microsoft Excel, treats -x^y as (-x)^y on the spreadsheet. Try it! (The 600 pound gorilla acknowledges the "error" but has no intention of fixing it and possibly breaking millions of existing spreadsheets). Interestingly enough, the macro language built in Excel, VBA, treats -x^y properly as -(x^y).

just in case you were wondering....
_________________

Best,

AkamaiBrah
Former Senior Instructor, Manhattan GMAT and VeritasPrep
Vice President, Midtown NYC Investment Bank, Structured Finance IT
MFE, Haas School of Business, UC Berkeley, Class of 2005
MBA, Anderson School of Management, UCLA, Class of 1993

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Re: practice problem   [#permalink] 15 Aug 2003, 07:54
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# practice problem

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