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Topic: Please remind me why -3^2 = -9
Replies: 26   Last Post: Nov 18, 2012 7:51 PM

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Beth Hentges

Posts: 104
Registered: 10/16/06
Re: Please remind me why -3^2 = -9
Posted: Nov 14, 2012 11:15 PM
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(-3)^2 is clear

- -(3^2) is clear

We have to choose which we mean when we write the following.

- -3^2

The reason we choose -3^2 to mean -(3^2) is because we do powers before multiplication and because -a = -1*a.

(-3)^2 = (-1*3)^2 , and the parentheses tell us to do the multiplication first.

- -(3^2) = -1*(3^2), and the parentheses tell us to do the power first.

- -3^2 = -1*3^2, and we do powers before multiplication.


As for PEMDAS, I use PEMA. Otherwise, students think PEMDAS says to do multiplication before division. Also, when I write it in words, for the E for exponents (which really should be another P for powers), I write, "Do exponents and roots from left to right." So, even if I did use PEMDAS it would be PERMDAS. Then, we also have to be careful with absolute value as well.

Beth in MN
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Date Subject Author
10/18/12
Read Please remind me why -3^2 = -9
Phil Mahler
10/18/12
Read Re: Please remind me why -3^2 = -9
John Peterson
10/18/12
Read Re: Please remind me why -3^2 = -9
Guy Brandenburg
10/18/12
Read RE: Please remind me why -3^2 = -9
Wayne Mackey
10/18/12
Read RE: Please remind me why -3^2 = -9
Phil Mahler
10/18/12
Read RE: Please remind me why -3^2 = -9
RotmanJ
10/18/12
Read Re: Please remind me why -3^2 = -9
Paul Hertzel
10/18/12
Read Re: Please remind me why -3^2 = -9
Phil Mahler
10/18/12
Read Re: Please remind me why -3^2 = -9
Clyde Greeno
10/19/12
Read Re: Please remind me why -3^2 = -9
Clyde Greeno
10/19/12
Read Re: Please remind me why -3^2 = -9
Alain Schremmer
10/19/12
Read RE: Please remind me why -3^2 = -9
Wayne Mackey
10/19/12
Read Re: Please remind me why -3^2 = -9
Alain Schremmer
10/19/12
Read Re: Please remind me why -3^2 = -9
Clyde Greeno
10/19/12
Read Re: Please remind me why -3^2 = -9
Alain Schremmer
10/21/12
Read RE: Please remind me why -3^2 = -9
Wayne Mackey
11/14/12
Read Re: Please remind me why -3^2 = -9
Beth Hentges
11/15/12
Read Re: Please remind me why -3^2 = -9
Clyde Greeno
11/16/12
Read Re: Please remind me why -3^2 = -9
Alain Schremmer
10/18/12
Read RE: Please remind me why -3^2 = -9
Collinge, Peter (Mathematics)
10/18/12
Read Re: Please remind me why -3^2 = -9
Guy Brandenburg
10/18/12
Read Re: Please remind me why -3^2 = -9
Phil Mahler
10/18/12
Read Re: Please remind me why -3^2 = -9
Alain Schremmer
11/18/12
Read Re: Please remind me why -3^2 = -9
EddieC
11/18/12
Read RE: Please remind me why -3^2 = -9
Matthews, George
11/18/12
Read Re: Please remind me why -3^2 = -9
Phil Mahler
11/18/12
Read Re: Please remind me why -3^2 = -9
Alain Schremmer

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