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Use the intermediate value theorem to show that the polynomial function has a real zero between the numbers [tex]-4[/tex] and [tex]-3[/tex].

[tex]
\begin{array}{l}
f(x) = x^4 - 6x^3 - 30x^2 + 48x + 136 \\
f(-4) = \square \quad \text{(Simplify your answer. Type an integer or a fraction.)} \\
f(-3) = \square \quad \text{(Simplify your answer. Type an integer or a fraction.)} \\
\end{array}
[/tex]

Since [tex]f(-4)[/tex] is positive and [tex]f(-3)[/tex] is negative, the signs change between [tex]f(-4)[/tex] and [tex]f(-3)[/tex]. This shows that

A. The zeros are [tex]-4[/tex] and [tex]-3[/tex].
B. A zero of the polynomial lies between [tex]-4[/tex] and [tex]-3[/tex].
C. The polynomial has 4 real zeros.


Sagot :

To show that the polynomial function [tex]\( f(x) = x^4 - 6x^3 - 30x^2 + 48x + 136 \)[/tex] has a real zero between the numbers [tex]\( -4 \)[/tex] and [tex]\( -3 \)[/tex], we will use the Intermediate Value Theorem. The Intermediate Value Theorem states that if a function [tex]\( f \)[/tex] is continuous on a closed interval [tex]\([a, b]\)[/tex] and if [tex]\( f(a) \)[/tex] and [tex]\( f(b) \)[/tex] have opposite signs, then there is at least one [tex]\( c \)[/tex] in the interval [tex]\((a, b)\)[/tex] such that [tex]\( f(c) = 0 \)[/tex].

First, let's calculate the value of the polynomial at [tex]\( x = -4 \)[/tex]:

[tex]\[ f(-4) = (-4)^4 - 6(-4)^3 - 30(-4)^2 + 48(-4) + 136 \][/tex]

Simplifying this step-by-step:

[tex]\[ (-4)^4 = 256 \][/tex]
[tex]\[ -6(-4)^3 = -6(-64) = 384 \][/tex]
[tex]\[ -30(-4)^2 = -30(16) = -480 \][/tex]
[tex]\[ 48(-4) = -192 \][/tex]

Adding these results together:

[tex]\[ f(-4) = 256 + 384 - 480 - 192 + 136 = 104 \][/tex]

So, [tex]\( f(-4) = 104 \)[/tex].

Next, let's calculate the value of the polynomial at [tex]\( x = -3 \)[/tex]:

[tex]\[ f(-3) = (-3)^4 - 6(-3)^3 - 30(-3)^2 + 48(-3) + 136 \][/tex]

Simplifying this step-by-step:

[tex]\[ (-3)^4 = 81 \][/tex]
[tex]\[ -6(-3)^3 = -6(-27) = 162 \][/tex]
[tex]\[ -30(-3)^2 = -30(9) = -270 \][/tex]
[tex]\[ 48(-3) = -144 \][/tex]

Adding these results together:

[tex]\[ f(-3) = 81 + 162 - 270 - 144 + 136 = -35 \][/tex]

So, [tex]\( f(-3) = -35 \)[/tex].

Since [tex]\( f(-4) = 104 \)[/tex] is positive and [tex]\( f(-3) = -35 \)[/tex] is negative, the signs change between [tex]\( f(-4) \)[/tex] and [tex]\( f(-3) \)[/tex]. According to the Intermediate Value Theorem, this indicates that there is at least one zero of the polynomial between [tex]\( -4 \)[/tex] and [tex]\( -3 \)[/tex].

Therefore, the correct answer is:
[tex]\[ \boxed{\text{B. A zero of the polynomial lies between -4 and -3.}} \][/tex]
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