Access Point #: MAFS.912.A-REI.2.AP.4a (Archived Access Point)


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Solve quadratic equations by completing the square.

Clarifications:

Essential Understandings

Concrete:

  • Count the number of terms in a quadratic equation.
  • Identify the numbers in the equation that would be used to complete the square.
  • Multiply and divide numbers using appropriate tools.
  • Use appropriate tools to calculate squares and square roots.
  • Order the steps for solving an equation using completing the square.
  • Perform operations on fractions.
  • Simplify fractions.
Representation:
  • Simplify radicals.
  • Calculate using multiple operations.
  • Substitute numbers from the equation into a template for completing the square.
  • Calculate squares and square roots using appropriate tools.
  • Determine the root from adding the terms.
  • Determine the root from subtracting the terms.
  • Understand the following vocabulary and concepts: + symbol, factor, coefficient, terms, exponent, base, constant, variable, binomial, monomial, polynomial, square, square root.
  • Move the constants to the same side of the equation.
  • Take half the middle term, square it, and add to both sides of equal sign.
  • Factor the left side into a perfect square.
  • Take the square root of both sides.
  • Solve for x.
    For example:
    begin mathsize 12px style x squared space plus space 6 x space minus space 16 space equals space 0 end style

    begin mathsize 12px style x squared space plus space 6 x space equals space 16 end style

    begin mathsize 12px style x squared space plus space 6 x space plus space 9 space equals space 16 space plus space 9 end style

    begin mathsize 12px style x squared space plus space 6 x space plus 9 space equals space 25 end style

    begin mathsize 12px style open parentheses x space plus 3 close parentheses squared space equals space 25 end style

    begin mathsize 12px style square root of left parenthesis x space plus space 3 right parenthesis squared end root space equals space square root of 25 end style

    begin mathsize 12px style x space plus space 3 space equals space plus-or-minus 5 end style

    begin mathsize 12px style x space equals space minus 5 space minus space 3 comma space x space equals space 5 space minus space 3 end style

    begin mathsize 12px style x space equals space minus 8 comma space 2 end style

     

Number: MAFS.912.A-REI.2.AP.4a Category: Access Points
Date Adopted or Revised: 07/14 Cluster: Solve equations and inequalities in one variable. (Algebra 1 - Major Cluster) (Algebra 2 - Supporting Cluster)

Clusters should not be sorted from Major to Supporting and then taught in that order. To do so would strip the coherence of the mathematical ideas and miss the opportunity to enhance the major work of the grade with the supporting clusters.

Related Standards

Name Description
MAFS.912.A-REI.2.4: Solve quadratic equations in one variable.
  1. Use the method of completing the square to transform any quadratic equation in x into an equation of the form (x – p)² = q that has the same solutions. Derive the quadratic formula from this form.
  2. Solve quadratic equations by inspection (e.g., for x² = 49), taking square roots, completing the square, the quadratic formula and factoring, as appropriate to the initial form of the equation. Recognize when the quadratic formula gives complex solutions and write them as a ± bi for real numbers a and b.



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