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HelicopterOff Topics › Out of Algebra practice, help me out
11-30-2007 05:46 AM  10 years agoPost 21
eggmcmuffinplz

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there for, b=0

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11-30-2007 05:55 AM  10 years agoPost 22
legoman67

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i end up with b = a which is correct....

he soved the problem harder then he needed too..

equiv
a * a * -b * -b = a * a * -a * -b

a,a,-b are on both so they cross out/cancel out, leaving with -b = -a

divide by -1 and you get a = b

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11-30-2007 06:14 AM  10 years agoPost 23
dkshema

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helibill wins because he got the answer first. There's no need to talk about dividing by zero or black magic.

a^2 - b^2 = a^2 -ab

Subtract a^2 from both sides of the equal sign. A legal operation -- you can do whatever you want to the left side of the equal sign as long as you do exactly the same thing to the other side. Subtracting "a squared" from both sides is correct.

It leaves:

-b^2 = -ab

divide both sides by -b. A legal operation, as you are doing the same thing to both sides of the equal sign, dividing by "b".

leaves b = a

and as stated initially, a = b = 1

and of course, simply plugging 1 in for a and b in the original equation yields:

1^2 - 1^2 = 1^2 - 1*1

1 - 1 = 1 - 1

0 = 0

Wow. No rocket science here, simple math. Not even a trick.

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11-30-2007 06:20 AM  10 years agoPost 24
EvoFlight50

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You guys aren't answering the question though. The question is look at the problem and find out what he did wrong algebraically. It's not solve it a different way to show it's wrong. Obviously we can plug 1 into the regular equation, or start subtracting stuff from each side right off the bat.

The question want's to know what he did wrong algebraically.

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11-30-2007 06:44 AM  10 years agoPost 25
dkshema

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Cedar Rapids, IA

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BTW. If you start with the assumption that a = b = 1, then the trick step of divding both sides by (a-b) blows the whole thing. That's where the trick division by zero comes into play.

It's the initial assumption that bites you in the trick step of dividing both sides.

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HelicopterOff Topics › Out of Algebra practice, help me out
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