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Find a polynomial function with the zeros -2​, 3​, 5 whose graph passes through the point (6,48)

Respuesta :

Answer:

f(x) = 2x³ - 12x² - 2x + 60

Step-by-step explanation:

Given that the zeros are x = - 2, x = 3, x = 5 , then the factors are

(x + 2), (x - 3), (x - 5)

The polynomial is then the product of the factors, that is

f(x) = a(x + 2)(x - 3)(x - 5) ← a is a multiplier

To find a substitute (6, 48) into the polynomial

48 = a(8)(3)(1) = 24a ( divide both sides by 24 )

a = 2 , thus

f(x) = 2(x + 2)(x - 3)(x - 5) ← expand the last 2 factors using FOIL

     = 2(x + 2)(x² - 8x + 15) ← distribute the parenthesis

     = 2(x³ - 8x² + 15x + 2x² - 16x + 30)

     = 2(x³ - 6x² - x + 30) ← distribute by 2

     = 2x³ - 12x² - 2x + 60

Using the factor theorem, it is found that the polynomial function is given by:

[tex]p(x) = 2(x^3 - 6x^2 - x + 30)[/tex]

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Factor theorem:

Given a polynomial f(x), this polynomial has roots [tex]x_{1}, x_{2}, x_{n}[/tex] such that it can be written as: [tex]a(x - x_{1})*(x - x_{2})*...*(x-x_n)[/tex], in which a is the leading coefficient.

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  • Zeros of -2, 3 and 5 mean that [tex]x_1 = -2, x_2 = 3, x_3 = 5[/tex]

The polynomial is given by:

[tex]p(x) = a(x - x_1)(x - x_2)(x-x_3)[/tex]

[tex]p(x) = a(x - (-2))(x - 3)(x - 5)[/tex]

[tex]p(x) = a(x + 2)(x - 3)(x - 5)[/tex]

[tex]p(x) = a(x^2 - x - 6)(x - 5)[/tex]

[tex]p(x) = a(x^3 - 6x^2 - x + 30)[/tex]

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  • It passes through the point (6,48), thus when [tex]x = 6, p(x) = 48[/tex].
  • This is used to find the leading coefficient.

[tex]p(x) = a(x^3 - 6x^2 - x + 30)[/tex]

[tex]48 = a(6^3 - 6(6)^2 - (6) + 30)[/tex]

[tex]24a = 48[/tex]

[tex]a = \frac{48}{24}[/tex]

[tex]a = 2[/tex]

Thus, the polynomial is given by:

[tex]p(x) = 2(x^3 - 6x^2 - x + 30)[/tex]

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