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Which polynomial function [tex][tex]$f(x)$[/tex][/tex] has a leading coefficient of 1, roots -4, 2, and 9 with multiplicity 1, and root -5 with multiplicity 3?

A. [tex]f(x) = 3(x + 5)(x + 4)(x - 2)(x - 9)[/tex]
B. [tex]f(x) = 3(x - 5)(x - 4)(x + 2)(x + 9)[/tex]
C. [tex]f(x) = (x + 5)(x + 5)(x + 5)(x + 4)(x - 2)(x - 9)[/tex]
D. [tex]f(x) = (x - 5)(x - 5)(x - 5)(x - 4)(x + 2)(x + 9)[/tex]

Sagot :

To determine which polynomial function [tex]\( f(x) \)[/tex] has the specified roots and multiplicities, we need to ensure the polynomial meets the given criteria:
- Leading coefficient of 1
- Roots [tex]\(-4, 2\)[/tex], and [tex]\(9\)[/tex] with multiplicity 1
- Root [tex]\(-5\)[/tex] with multiplicity 3

We'll construct the polynomial step-by-step:

1. Identify the factors for each root:
- A root [tex]\( r \)[/tex] of a polynomial translates to a factor of [tex]\( (x - r) \)[/tex].
- For the root [tex]\(-4\)[/tex] with multiplicity 1: the factor is [tex]\( (x + 4) \)[/tex].
- For the root [tex]\(2\)[/tex] with multiplicity 1: the factor is [tex]\( (x - 2) \)[/tex].
- For the root [tex]\(9\)[/tex] with multiplicity 1: the factor is [tex]\( (x - 9) \)[/tex].
- For the root [tex]\(-5\)[/tex] with multiplicity 3: the factor is [tex]\( (x + 5)^3 \)[/tex].

2. Combine all factors to form the polynomial:
[tex]\[ f(x) = (x + 5)^3 (x + 4) (x - 2) (x - 9) \][/tex]

3. Check the leading coefficient:
- The polynomial [tex]\( f(x) = (x + 5)^3 (x + 4) (x - 2) (x - 9) \)[/tex] has a leading coefficient of 1, since all coefficients involve a basic unscaled binomial [tex]\( (x - r) \)[/tex].

4. Match given options with our polynomial:
- Option 1: [tex]\(3(x+5)(x+4)(x-2)(x-9)\)[/tex]
- This polynomial does not match as it scales the factors by 3 and does not have [tex]\( (x+5)^3 \)[/tex].
- Option 2: [tex]\(3(x-5)(x-4)(x+2)(x+9)\)[/tex]
- This polynomial has entirely different roots and does not match.
- Option 3: [tex]\((x+5)(x+5)(x+5)(x+4)(x-2)(x-9)\)[/tex]
- This polynomial matches perfectly with [tex]\((x+5)^3(x+4)(x-2)(x-9)\)[/tex].
- Option 4: [tex]\((x-5)(x-5)(x-5)(x-4)(x+2)(x+9)\)[/tex]
- This polynomial has entirely different roots and does not match.

Since Option 3 is the one that matches our constructed polynomial, the answer is:
[tex]\[ \boxed{(x+5)(x+5)(x+5)(x+4)(x-2)(x-9)} \][/tex]