A polynomial function has a root of -7 with multiplicity 2, a root of -1 with multiplicity 1, a root 2 of multiplicity 4. And a root of 4 with multiplicity 1. If the function has a positive leading coefficient and is of even degree, which statement about the graph is true?

A. The graph of the function is positive on (2,4)
B. The graph of the function is negative on (4, ∞)
C. The graph of the function is positive on (-∞, -7)
D. The graph of the function is negative on (-7, -1)

Respuesta :

From the information given in the problem, our function will be
[tex]f(x)=a(x+7)^2(x+1)(x-2)^4(x-4)[/tex]
where [tex]a[/tex] is a positive leading coefficient.

Now, we just need to go through the answer choices and plug in x values that are in each interval.

A) 3 is between (2,4) so let's test [tex]f(3)[/tex]
[tex]f(3)=-400a[/tex]
[tex]-400a[/tex] is not a positive number, so A is wrong

B) [tex]f(5)=69984a[/tex]
[tex]69984a[/tex] is not a negative number, so B is also wrong.

C) [tex]f(-8)=840,000a[/tex]
[tex]840,000a[/tex] is a positive number, so C is correct.

D) Just to make sure, let's check D.
[tex]f(-2)=38400a[/tex]
[tex]38400a[/tex] is not a negative number, so D is also wrong.

Polynomials are expressions that uses variables, constants and exponents.

The correct statement is: (c) The graph of the function is positive on (-∞, -7)

The given parameters are:

[tex]\mathbf{(Root, Multiplicity) = (-7,2)}[/tex]

This means that: [tex]\mathbf{(x + 7)^2}[/tex]

[tex]\mathbf{(Root, Multiplicity) = (-1,1)}[/tex]

This means that: [tex]\mathbf{(x + 1)^1}[/tex]

[tex]\mathbf{(Root, Multiplicity) = (2,4)}[/tex]

This means that: [tex]\mathbf{(x - 1)^4}[/tex]

[tex]\mathbf{(Root, Multiplicity) = (4,1)}[/tex]

This means that: [tex]\mathbf{(x - 4)^1}[/tex]

So, the polynomial is:

[tex]\mathbf{P(x) = a(x + 7)^4(x + 1)^1(x - 1)^4(x - 4)^1}[/tex]

[tex]\mathbf{P(x) = a(x + 7)^4(x + 1)(x - 1)^4(x - 4)}[/tex]

Rearrange

[tex]\mathbf{P(x) = a(x + 7)^4(x - 1)^4(x + 1)(x - 4)}[/tex]

Next, we test the options

(a) The graph of the function is positive on (2,4)

Use x = 3

[tex]\mathbf{P(3) = a(3 + 7)^4(3 - 1)^4(3 + 1)(3 - 4)}[/tex]

[tex]\mathbf{P(3) = -640000a}[/tex]

The above is a negative number

So, (a) is false

(b) The graph of the function is negative on (4, ∞)

Use x = 6

[tex]\mathbf{P(6) = a(6 + 7)^4(6 - 1)^4(6 + 1)(6 - 4)}[/tex]

[tex]\mathbf{P(6) = 249908750a}[/tex]

The above is a positive number.

So, (b) is false

(c) The graph of the function is positive on (-∞, -7)

Use x = -8

[tex]\mathbf{P(-8) = a(-8 + 7)^4(-8 - 1)^4(-8 + 1)(-8 - 4)}[/tex]

[tex]\mathbf{P(-8) = 551124a}[/tex]

The above is a positive number.

So, (c) is false

Hence, the correct statement is: (c) The graph of the function is positive on (-∞, -7)

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