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3. Find [tex]\((f \cdot g)(x)\)[/tex] if [tex]\(f(x) = 7x^3 - 5x^2 + 42x - 30\)[/tex] and [tex]\(g(x) = 7x - 5\)[/tex].

A. [tex]\(49x^4 + 70x^3 - 319x^2 + 420x - 150\)[/tex]
B. [tex]\(49x^4 - 70x^3 + 319x^2 - 420x + 150\)[/tex]
C. [tex]\(49x^4 - 269x^2 - 150\)[/tex]
D. [tex]\(49x^4 + 269x^2 + 150\)[/tex]

Answer :

To find [tex]\((f \cdot g)(x)\)[/tex], where [tex]\(f(x) = 7x^3 - 5x^2 + 42x - 30\)[/tex] and [tex]\(g(x) = 7x - 5\)[/tex], we need to multiply the two functions together. Let's go through the steps:

1. Set Up the Multiplication:
We need to multiply each term of [tex]\(f(x)\)[/tex] by each term of [tex]\(g(x)\)[/tex]. This means calculating each term generated by multiplying terms from [tex]\(f(x)\)[/tex] with the term from [tex]\(g(x)\)[/tex]:

[tex]\[
(7x^3 - 5x^2 + 42x - 30) \cdot (7x - 5)
\][/tex]

2. Distribute the Terms:
- Multiply [tex]\(7x^3\)[/tex] by each term in [tex]\(g(x)\)[/tex]:
[tex]\[
7x^3 \cdot 7x = 49x^4
\][/tex]
[tex]\[
7x^3 \cdot (-5) = -35x^3
\][/tex]

- Multiply [tex]\(-5x^2\)[/tex] by each term in [tex]\(g(x)\)[/tex]:
[tex]\[
-5x^2 \cdot 7x = -35x^3
\][/tex]
[tex]\[
-5x^2 \cdot (-5) = 25x^2
\][/tex]

- Multiply [tex]\(42x\)[/tex] by each term in [tex]\(g(x)\)[/tex]:
[tex]\[
42x \cdot 7x = 294x^2
\][/tex]
[tex]\[
42x \cdot (-5) = -210x
\][/tex]

- Multiply [tex]\(-30\)[/tex] by each term in [tex]\(g(x)\)[/tex]:
[tex]\[
-30 \cdot 7x = -210x
\][/tex]
[tex]\[
-30 \cdot (-5) = 150
\][/tex]

3. Combine All Terms:
Now, add all the terms together:
[tex]\[
49x^4 + (-35x^3 - 35x^3) + (25x^2 + 294x^2) + (-210x - 210x) + 150
\][/tex]

4. Simplify:
- Combine like terms:
[tex]\[
49x^4 - 70x^3 + 319x^2 - 420x + 150
\][/tex]

So, [tex]\((f \cdot g)(x) = 49x^4 - 70x^3 + 319x^2 - 420x + 150\)[/tex].

This matches with the given options, making the correct choice: [tex]\(49x^4 - 70x^3 + 319x^2 - 420x + 150\)[/tex].

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