Pretest: Relationships Between Functions

Select the correct answer.

Given the functions [tex] f(x) [/tex] and [tex] g(x) [/tex]:

[tex]\[ \begin{array}{l}
f(x) = 11x^3 - 3x^2 \\
g(x) = 7x^4 + 9x^3
\end{array} \][/tex]

Which expression is equal to [tex] f(x) \cdot g(x) [/tex]?

A. [tex] 7x^4 + m x^3 - 3x^2 [/tex]
B. [tex] \pi x^{12} + 99x^3 - 21x^4 - 27x^4 [/tex]
C. [tex] 18x^7 + 10x^4 + 6x^5 [/tex]
D. [tex] 77x^7 + 78x^4 - 27x^3 [/tex]



Answer :

To find the product of the two given functions [tex]\( f(x) \)[/tex] and [tex]\( g(x) \)[/tex], follow these steps:

1. Identify the given functions:
[tex]\[ f(x) = 11x^3 - 3x^2 \][/tex]
[tex]\[ g(x) = 7x^4 + 9x^3 \][/tex]

2. Multiply [tex]\( f(x) \)[/tex] and [tex]\( g(x) \)[/tex]:

When you multiply two polynomials, you distribute each term in the first polynomial by each term in the second polynomial.

Let’s distribute each term:

[tex]\[ (11x^3 - 3x^2) \cdot (7x^4 + 9x^3) \][/tex]

- Multiply [tex]\( 11x^3 \)[/tex] by each term in [tex]\( (7x^4 + 9x^3) \)[/tex]:
[tex]\[ 11x^3 \cdot 7x^4 = 77x^7 \][/tex]
[tex]\[ 11x^3 \cdot 9x^3 = 99x^6 \][/tex]

- Multiply [tex]\( -3x^2 \)[/tex] by each term in [tex]\( (7x^4 + 9x^3) \)[/tex]:
[tex]\[ -3x^2 \cdot 7x^4 = -21x^6 \][/tex]
[tex]\[ -3x^2 \cdot 9x^3 = -27x^5 \][/tex]

3. Combine like terms:

Now, combine all the products you have calculated:
[tex]\[ 77x^7 + 99x^6 - 21x^6 - 27x^5 \][/tex]

Simplify the like terms:
[tex]\[ 77x^7 + (99x^6 - 21x^6) - 27x^5 \][/tex]
[tex]\[ 77x^7 + 78x^6 - 27x^5 \][/tex]

4. Compare to the given options:

Look at the choices provided to find the matching expression:

A. [tex]\( 7x^4 + mx^3 - 3x^2 \)[/tex]

B. [tex]\( \pi x^{12} + 99x^3 - 21x^4 - 27x^4 \)[/tex]

C. [tex]\( 18x^7 + 10x^4 + 6x^5 \)[/tex]

D. [tex]\( 77x^7 + 78x^6 - 27x^5 \)[/tex]

The correct expression that matches the product [tex]\( 77x^7 + 78x^6 - 27x^5 \)[/tex] is:

[tex]\[ \boxed{D} \][/tex]