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#1 2012-12-19 13:01:58

Frublox
Member
Registered: 2012-12-19
Posts: 1

Square root problem

Got this problem on a test:
          ____
12 + √2x-1 = 4

Okay, so then I subtract 12 from both sides:
  ____
√2x-1 = -8
2x - 1 = 64   I then square both sides...
2x = 65        Add 1 to each side
x = 65/2       Divide both sides by two.

However, that answer doesn't work. Are there simply no solutions, then?

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#2 2012-12-19 14:21:46

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 88,589

Re: Square root problem

Hi Frublox;

That is correct, there are no solutions. Not every equation is a true statement. You always check the validity of your answer by plugging into the original equation.

Please go here:

http://www.mathsisfun.com/algebra/radic … lving.html


In mathematics, you don't understand things. You just get used to them.

I agree with you regarding the satisfaction and importance of actually computing some numbers. I can't tell you how often I see time and money wasted because someone didn't bother to run the numbers.

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#3 2012-12-19 20:45:43

bob bundy
Moderator
Registered: 2010-06-20
Posts: 6,466

Re: Square root problem

hi Frublox

That answer is the solution to

-12 + √(2x-1) = -4

When you square you cannot help but introduce 'solutions' to this alternative equation as well so you were right to check the value you had.

Bob


You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei

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#4 2012-12-19 21:25:17

anonimnystefy
Real Member
From: The Foundation
Registered: 2011-05-23
Posts: 15,600

Re: Square root problem

Even when you got √2x-1 = -8 you could've said that there are no solutions, because a square root of a positive number is always positive...


“Here lies the reader who will never open this book. He is forever dead.

“Taking a new step, uttering a new word, is what people fear most.” ― Fyodor Dostoyevsky, Crime and Punishment

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#5 2012-12-19 21:31:14

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 88,589

Re: Square root problem

Hi;

Yes, it always takes the principal value.


In mathematics, you don't understand things. You just get used to them.

I agree with you regarding the satisfaction and importance of actually computing some numbers. I can't tell you how often I see time and money wasted because someone didn't bother to run the numbers.

Online

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