Tuesday, January 13, 2009


Today in algebra II, we were learning to solve polynomial equations by factoring. When factoring a sum or difference of two cubes, I begin with the formal patterns and then I give my students a mnemonic to help them remember the pattern. I tell my students to remember how to factor the sum or difference of two cubes, just remember the word SOFAS.

For example to factor x^3 + 125, we get our binomial factor of (x + 5) and then we use SOFAS

S (Square the front) x^2
O (opposite sign) x^2 -
F (Front times back) x^2 - 5x
A (Always Positive) x^2 - 5x +
S (Square the Back) x^2 - 5x + 25

Answer: (x + 5)(x^2 - 5x + 25)

To help the students remember SOFAS, we draw a little poster with a picture of a sofa and then write out an example showing how to use SOFA. I know this little activity helps them, because the Precal teacher told me at the beginning of the school year that my students from last year taught her this and she was so excited that they actually remembered something from the previous year.


*M* said...

Unrelated but I am in love with your avatar on Blogger: cancelling out the 2s! It's such a hair-pulling exercise, teaching students what they're not allowed to do with algebraic fractions.

Mrs. H said...

Thanks M, I've been meaning to change it. I've just been too lazy.

Susan said...

Its looking fine, you can find more Sofas here…..

Susan said...

Its looking fine, you can find more Sofas here…..

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