Polynomial long division
Same algorithm as numerical long division — divide, multiply, subtract, bring down.
Algorithm. To divide by ():
- Divide the leading term of by the leading term of — gives the first term of the quotient.
- Multiply by that quotient term.
- Subtract from .
- Bring down the next term and repeat.
Stop when the running remainder has degree less than .
Worked walkthrough. Divide by .
2x^2 - x + 5
┌───────────────────────────────
x - 2 │ 2x^3 - 5x^2 + 7x - 9
2x^3 - 4x^2
─────────────
-x^2 + 7x
-x^2 + 2x
─────────────
5x - 9
5x - 10
─────────
1
So .
Identity check. Always verify by expansion: . Add the remainder to get . ✓
Comparing coefficients (alternative). If you write and expand, you can solve for , , by matching coefficients. For exam efficiency, whichever method you find faster is fine — Edexcel mark schemes accept both.
- Divide-multiply-subtract-bring down (DMSB).
- Stop when remainder degree divisor degree.
- Always verify by expansion.
- Comparing coefficients is an equally-accepted alternative.