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Determine the equations for the cubic functions given their x-intercepts and a point on each graph.

Mathematics

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Okay, asanda, let's determine the equations for these cubic functions. The general form is y=ax3+bx2+cx+dy = ax^3 + bx^2 + cx + d. We'll use the x-intercepts and a given point to find the specific equation for each graph.

Graph (1)

  1. Identify x-intercepts and their multiplicity.

    The graph touches the x-axis at x=−1x=-1, indicating a double root (multiplicity 2). It crosses the x-axis at x=3x=3, indicating a single root.
    The factored form is y=a(x+1)2(x−3)y = a(x+1)^2(x-3).

  2. Use the given point (2,−6)(2, -6) to find aa.

    Substitute x=2x=2 and y=−6y=-6 into the equation:

    −6=a(2+1)2(2−3)-6 = a(2+1)^2(2-3) −6=a(3)2(−1)-6 = a(3)^2(-1) −6=a(9)(−1)-6 = a(9)(-1) −6=−9a-6 = -9a a=−6−9=23a = \frac{-6}{-9} = \frac{2}{3}
  3. Write the equation in factored form and expand.

    y=23(x+1)2(x−3)y = \frac{2}{3}(x+1)^2(x-3)

    Expand (x+1)2(x+1)^2:

    (x+1)2=x2+2x+1(x+1)^2 = x^2 + 2x + 1

    Multiply by (x−3)(x-3):

    (x2+2x+1)(x−3)=x3−3x2+2x2−6x+x−3(x^2 + 2x + 1)(x-3) = x^3 - 3x^2 + 2x^2 - 6x + x - 3 =x3−x2−5x−3= x^3 - x^2 - 5x - 3

    Multiply by 23\frac{2}{3}:

    y=23(x3−x2−5x−3)y = \frac{2}{3}(x^3 - x^2 - 5x - 3) \boxed{\text{y = \frac{2}{3}x^3 - \frac{2}{3}x^2 - \frac{10}{3}x - 2}}

    Graph (2)

  4. Identify x-intercepts and their multiplicity.

    The graph crosses the x-axis at x=−2x=-2, indicating a single root. It touches the x-axis at x=3x=3, indicating a double root.
    The factored form is y=a(x+2)(x−3)2y = a(x+2)(x-3)^2.

  5. Use the given point (0,−18)(0, -18) to find aa.

    Substitute x=0x=0 and y=−18y=-18 into the equation:

    −18=a(0+2)(0−3)2-18 = a(0+2)(0-3)^2 −18=a(2)(−3)2-18 = a(2)(-3)^2 −18=a(2)(9)-18 = a(2)(9) −18=18a-18 = 18a a=−1818=−1a = \frac{-18}{18} = -1
  6. Write the equation in factored form and expand.

    y=−1(x+2)(x−3)2y = -1(x+2)(x-3)^2

    Expand (x−3)2(x-3)^2:

    (x−3)2=x2−6x+9(x-3)^2 = x^2 - 6x + 9

    Multiply by (x+2)(x+2):

    (x+2)(x2−6x+9)=x3−6x2+9x+2x2−12x+18(x+2)(x^2 - 6x + 9) = x^3 - 6x^2 + 9x + 2x^2 - 12x + 18 =x3−4x2−3x+18= x^3 - 4x^2 - 3x + 18

    Multiply by −1-1:

    y=−(x3−4x2−3x+18)y = -(x^3 - 4x^2 - 3x + 18) \boxed{\text{y = -x^3 + 4x^2 + 3x - 18}}

    Graph (3)

  7. Identify x-intercepts and their multiplicity.

    The graph crosses the x-axis at x=−4x=-4, indicating a single root. It touches the x-axis at x=0x=0, indicating a double root.
    The factored form is y=a(x+4)(x−0)2y = a(x+4)(x-0)^2, which simplifies to y=ax2(x+4)y = ax^2(x+4).

  8. Use the given point (−2,4)(-2, 4) to find aa.

    Substitute x=−2x=-2 and y=4y=4 into the equation:

    4=a(−2)2(−2+4)4 = a(-2)^2(-2+4) 4=a(4)(2)4 = a(4)(2) 4=8a4 = 8a a=48=12a = \frac{4}{8} = \frac{1}{2}
  9. Write the equation in factored form and expand.

    y=12x2(x+4)y = \frac{1}{2}x^2(x+4) y=12(x3+4x2)y = \frac{1}{2}(x^3 + 4x^2) \boxed{\text{y = \frac{1}{2}x^3 + 2x^2}}

    Graph (4)

  10. Identify x-intercepts and their multiplicity.

    The graph crosses the x-axis at x=0x=0, indicating a single root. It touches the x-axis at x=5x=5, indicating a double root.
    The factored form is y=a(x−0)(x−5)2y = a(x-0)(x-5)^2, which simplifies to y=ax(x−5)2y = ax(x-5)^2.

  11. Use the given point (1,−4)(1, -4) to find aa.

    Substitute x=1x=1 and y=−4y=-4 into the equation:

    −4=a(1)(1−5)2-4 = a(1)(1-5)^2 −4=a(1)(−4)2-4 = a(1)(-4)^2 −4=a(1)(16)-4 = a(1)(16) −4=16a-4 = 16a a=−416=−14a = \frac{-4}{16} = -\frac{1}{4}
  12. Write the equation in factored form and expand.

    y=−14x(x−5)2y = -\frac{1}{4}x(x-5)^2

    Expand (x−5)2(x-5)^2:

    (x−5)2=x2−10x+25(x-5)^2 = x^2 - 10x + 25

    Multiply by xx:

    x(x2−10x+25)=x3−10x2+25xx(x^2 - 10x + 25) = x^3 - 10x^2 + 25x

    Multiply by −14-\frac{1}{4}:

    y=−14(x3−10x2+25x)y = -\frac{1}{4}(x^3 - 10x^2 + 25x) \boxed{\text{y = -\frac{1}{4}x^3 + \frac{5}{2}x^2 - \frac{25}{4}x}}
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