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    Algebra
    Math Games
  • Decimals in Space
  • Fraction Balls
  • Integers in Space
  • Math Man
  • Number Balls
  • Geometry
    Interactive
    Trigonometry
    Jobs
  • Tutoring jobs
  • New York Tutoring Jobs
  • White Plains, NY
  • Westchester County, NY
  • Chicago Math Jobs
  • Philadelphia
  • Teacher Resources
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    Equation of a Parabola

    Standard Form and Vertex Form Equations

     Standard Form Equation 
    The standard form of a parabola's equation is generally expressed:
    • y = ax 2 + bx + c
      • The role of 'a'
        • If a> 0, the parabola opens upwards
        • if a< 0, it opens downwards.
      • The axis of symmetry
        • The axis of symmetry is the line x = -b/2a
    Standard Form Equation Role
     Vertex Form of Equation  
    The vertex form of a parabola's equation is generally expressed as :
    y= a(x-h)2+k
    • (h,k) is the vertex
    • If a is positive then the parabola opens upwards like a regular "U".
    • If a is negative, then the graph opens downwards like an upside down "U".
    • If |a| > 1, the graph of the parabola widens. This just means that the "U" shape of parabola stretches out sideways .
    • If |a| < 1, the graph of the graph becomes narrower(The effect is the opposite of |a| > 1).

    Practice Problems

    Vertex and Direction-Vertex Form Equation




    Part I

    1) What is the graph of the following parabola y = (x–1)² + 1?
    Answer


    2) What is the graph of the following parabola y = –(x–1)² + 1?
    Answer


    3) What is the graph of the following parabola y = (x+2)² –3?
    Answer

      Identifying the vertex in vertex form  



    1) What is the vertex of the following parabola:
    y = (x + 3)² + 4

    Answer


    2) Find the vertex of the following parabola:
    y = (x - 3)² + 4
    Answer


    3) What is the vertex of the parabola whose vertex form equation is
    y = (x - 2)² - 3


    Answer





    Part III

    1) What is the vertex of a parabola with the following equation:
    y=  2(x-3)2+4 ? Does the parabola open upwards or downwards?
     Answers  

    2) If a parabola's equation is  y =  3(x+3)2 +4, what is its vertex? Which way does it open?
     Answers  

    3) A parabola has the equation y = -22(x - 9)2 + 5. What is its vertex? Which way does the parabola open?
     Answers 

    Practice finding the axis of symmetry given the vertex form equation of a parabola
     Vertex from Standard Form Equation 


    The standard form equation of a parabola is
    y = ax² + bx + c
    To find the vertex of a parabola from the standard equation, use the following formula
    • The x corrdinate = -b/2a
    • To find the y coordinate substitute this value (-b/2a) into the equation



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