Difference between revisions of "Common factorizations"

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*<math>(a+b+c)^3=a^3+b^3+c^3+3(a+b)(b+c)(a+c)</math>
 
*<math>(a+b+c)^3=a^3+b^3+c^3+3(a+b)(b+c)(a+c)</math>
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== Advanced Factorizations ==
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*<math>a^3+b^3+c^3-3abc=(a+b+c)(a^2+b^2+c^2-ab-ac-bc)=(a+b+c)((a-b)^2+(b-c)^2+(c-a)^2)/2</math>
  
 
== Other Resources ==
 
== Other Resources ==

Revision as of 10:53, 3 May 2009

These are common factorizations that are used all the time. These should be memorized, but one should also know how they are derived.

Basic Factorizations

  • $x^2-y^2=(x+y)(x-y)$
  • $x^3+y^3=(x+y)(x^2-xy+y^2)$
  • $x^3-y^3=(x-y)(x^2+xy+y^2)$

Vieta's/Newton Factorizations

These factorizations are useful for problem that could otherwise be solved by Newton sums or problems that give a polynomial, and ask a question about the roots. Combined with Vieta's formulas, these are excellent factorizations that show up everywhere.

  • $(a+b+c)^2=a^2+b^2+c^2+2(ab+bc+ac)$
  • $(a+b+c)^3=a^3+b^3+c^3+3(a+b)(b+c)(a+c)$

Advanced Factorizations

  • $a^3+b^3+c^3-3abc=(a+b+c)(a^2+b^2+c^2-ab-ac-bc)=(a+b+c)((a-b)^2+(b-c)^2+(c-a)^2)/2$

Other Resources