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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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 Phil Mahler Posts: 126 Registered: 12/6/04
Please remind me why -3^2 = -9
Posted: Oct 18, 2012 5:37 AM
 att1.html (1.3 K)

I have been teaching a long time, and I know from experience that 50% of
students will tell me that ­3^2 = +9 on a test or a final, despite having
discussed it a few times in a course.

When I first started teaching I taught calculus and precalc. Piece of cake.
Then I started with an Algebra I class and couldn¹t connect at all for the
first week or so. I was ready to believe I couldn¹t teach. I simply could
not explain how I got the right answers when evaluating expressions... Then
I discovered the order of operations (PEMDAS to some). A definition of the
order of operations which I had so internalized that I didn¹t know there was
a rule for it. Since that discovery I¹ve been a wonderful teacher. :-)

So... I must be missing something that so many of my students think ­3^2 is
+9. What is the rule I have never discovered?

Full disclosure: I think ­k^2, k a constant, should be banned from
mathematics texts and tests. -x^2, x a variable, evaluated for say ­3,
absolutely (no pun intended) but not ­3^2.

Phil

Date Subject Author
10/18/12 Phil Mahler
10/18/12 John Peterson
10/18/12 Guy Brandenburg
10/18/12 Wayne Mackey
10/18/12 Phil Mahler
10/18/12 RotmanJ
10/18/12 Paul Hertzel
10/18/12 Phil Mahler
10/18/12 Clyde Greeno
10/19/12 Clyde Greeno
10/19/12 Alain Schremmer
10/19/12 Wayne Mackey
10/19/12 Alain Schremmer
10/19/12 Clyde Greeno
10/19/12 Alain Schremmer
10/21/12 Wayne Mackey
11/14/12 Beth Hentges
11/15/12 Clyde Greeno
11/16/12 Alain Schremmer
10/18/12 Collinge, Peter (Mathematics)
10/18/12 Guy Brandenburg
10/18/12 Phil Mahler
10/18/12 Alain Schremmer
11/18/12 EddieC
11/18/12 Matthews, George
11/18/12 Phil Mahler
11/18/12 Alain Schremmer