Math Is Fun Forum

Au101

Member

Registered: 2010-12-01

Posts: 353

Quick algebra question

Just a quick one to ask what is the best way to solve the following equation:

My approach was to say:

And then square both sides:

However, -3/4 obviously isn't a solution to:

If you take the principal value of the square root function and it is also not given as a solution by wolfram alpha.

So I was wondering if I went about this question the right way, or should I have done something different?

zetafunc

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Registered: 2014-05-21

Posts: 2,432

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Re: Quick algebra question

Yes, that's fine. When you square, you introduced the other solution, which does not satisfy the original equation -- which is why it's always important to check that your final result makes logical sense. (You sometimes also see this type of thing when doing kinematics problems -- you may end up getting a 'negative time' through solving a quadratic, which usually does have some physical meaning, but may be irrelevant to your problem.)

Last edited by zetafunc (2015-02-16 05:45:24)

Au101

Member

Registered: 2010-12-01

Posts: 353

Re: Quick algebra question

Thank you very much for your help

(This was just a part of a question in a differentiation exercise)