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Friday Algebra Quiz: Find The Roots

Haven't posted a quiz for a while. Tom Wheeler's post on the SLUUG mailing list about 100 Things Your Kids May Never Know About prompted me to go on the internet looking for some of the things I remembered from my childhood.

And hours later (you know how it goes: first you go crazy with Google searches, then you get sucked into Wikipedia following hundreds of must-follow links, etc.) I landed here:

It's a college algebra text book from 1904. Does this look like what your college-age kids can handle now? How about you? Are you up to it?

Q: What are the roots of the equation x3 - 9x - 28 = 0?

Strict rules apply: No Mathematica, Maple, MATLAB, WolframAlpha, or any computerized algebra tools.

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Posted by Weiqi Gao on July 24, 2009 12:41:06 PM CDT #


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Re: Friday Algebra Quiz: Find The Roots

Comment from Keith Sader on July 24, 2009 3:14:56 PM CDT #
I did have to look up the quadratic formula, but I managed to do the synthetic division correctly. I believe the roots are:
  • (x-4)
  • (x-2 + sqrt(3))
  • (x-2 - sqrt(11))
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Re: Friday Algebra Quiz: Find The Roots

Comment from You Xu on July 27, 2009 10:08:29 PM CDT #
I tried to plugin x=3, x=4, x=5, and yes, x=4 is a solution. Then, you can basically find out that x^3 - 9x -28 = (x-4)(x^2+4x +7). So the rest is easy.

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