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Maths
Lv 4
Maths asked in Science & MathematicsMathematics · 8 years ago

Find constants - Mathematics?

A maths problem

Find constants a, b and c such that, for all values of x,

3x² - 5x + 1 = a(x+b)² + c

Hence find the coordinates of the vertex on the graph of y=3x² - 5x + 1

Working and description helpful

Thanks

3 Answers

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  • 8 years ago
    Favorite Answer

    3x² - 5x + 1 = a(x+b)² + c

    3x² - 5x + 1 = ax² + 2ab.x + a.b² + c

    this is only possible if all powers of x vanish so:

    a = 3

    this gives

    - 5x + 1 = + 6b.x + 3.b² + c

    so b = -5/6

    this gives

    + 1 = + 25/12 + c

    so c = -13/12

    You can find the vertex (lowest value) of y = 3x² - 5x + 1 by differentiating

    dy/dx = 0 = 6.x - 5 so at x = 5/6

  • iceman
    Lv 7
    8 years ago

    y = 3(x^2 - 5/3*x + (5/6)^2) + 1 - 25/36

    y = 3(x - 5/6)^2 - 13/12 => in vertex form of : a(x - h)^2 + k, where (h , k) is the vertex:

    vertex at(5/6 , -13/12)

  • DWRead
    Lv 7
    8 years ago

    y = 3x² - 5x + 1

    you want to convert it to "vertex form," y = a(x - h)² + k

    factor out the leading coefficient

    y = 3(x² -(5/3)x) + 1

    complete the square

     coefficient of x term: -5/3

     divide coefficient in half: -5/6

     square it: (5/6)²

     use (5/6)² to complete the square:

    y = 3(x² -(5/3)x + (5/6)²) - 3(5/6)² + 1

     = 3(x - 5/6)² - 3(5/6)² + 1

     = 3(x - 5/6)² - 13/12

    vertex (5/6, -13/12)

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