Difference between revisions of "Completing the square"
(→Instructive Problem: AIME 1987 #5) |
m (Quadratic Formula -> Quadratic formula) |
||
| Line 22: | Line 22: | ||
<math>{x=\frac{-b \pm \sqrt{b^2-4ac}}{2a}}</math> | <math>{x=\frac{-b \pm \sqrt{b^2-4ac}}{2a}}</math> | ||
| − | This formula is also called the [[Quadratic | + | This formula is also called the [[Quadratic formula]]. |
===Applications of Adding and Factoring=== | ===Applications of Adding and Factoring=== | ||
Revision as of 09:22, 19 June 2006
Motivations
All quadratic equations in the form 
can be solved by taking the square root of b and subracting a. Completing the square is a technique to manipulate every quadratic into the easily solveable form above.
General Solution For A Quadratic by Completing the Square
Let the quadratic be in the form 
.
Moving c to the other side, we obtain
Dividing by 
and adding 
to both sides yields
.
Factoring the LHS gives
As described above, an equation in this form can be solved, yielding
This formula is also called the Quadratic formula.
Applications of Adding and Factoring
Other degrees of polynomials may be solved by adding constant terms and factoring.
Another common usage is in conic sections. The equations for conic sections typically contain a squared term such as 
. However, the problem may be posed as to convert from an expanded form to a factored perfect square. Completing the square is the standard method.
All kinds of exotic factoring techniques are used on the AIME, and completing the square is just one. The follow solution to AIME 1987 #5 is but one.
