Factoring
Note to readers and editers: Please fix up this page by adding in material from Joe's awesome factoring page.
Contents
Why Factor
Factoring equations is an essential part of problem solving. Applying number theory to products yields many results.
There are many ways to factor.
Differences and Sums of Powers
Using the formula for the sum of a geometric sequence, it's easy to derive the more general formula:
Take note of the specific case where n is odd:
This also leads to the formula for the sum of cubes,
Vieta's/Newton Factorizations
These factorizations are useful for problems 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.
Other Useful Factorizations
- See Simon's Favorite Factoring Trick (This is not a recognized formula, please do not quote it on contests)
- Binomial theorem
Practice Problems
- Prove that
is never divisible by 121 for any positive integer
.
- Prove that
is divisible by 7. - USSR Problem Book
- Factor
.