Question 1 (Essay Worth 4 points)

Is [tex]$x + 10$[/tex] a factor of the function [tex]$f(x) = x^3 - 75x + 250$[/tex]? Use the Remainder Theorem to justify your answer.



Answer :

Certainly, let's determine if [tex]\( x + 10 \)[/tex] is a factor of the function [tex]\( f(x) = x^3 - 75x + 250 \)[/tex] using the Remainder Theorem.

### Step-by-Step Solution:

1. Understanding the Remainder Theorem:
The Remainder Theorem states that for a polynomial [tex]\( f(x) \)[/tex], if we divide [tex]\( f(x) \)[/tex] by [tex]\( x - c \)[/tex], the remainder of this division is [tex]\( f(c) \)[/tex]. As a direct application, [tex]\( x - c \)[/tex] is a factor of [tex]\( f(x) \)[/tex] if and only if [tex]\( f(c) = 0 \)[/tex].

2. Identify the values in the problem:
We need to check if [tex]\( x + 10 \)[/tex] is a factor of [tex]\( f(x) = x^3 - 75x + 250 \)[/tex].
- Here, [tex]\( x + 10 \)[/tex] can be rewritten as [tex]\( x - (-10) \)[/tex].
- According to the Remainder Theorem, to check if [tex]\( x + 10 \)[/tex] is a factor, we need to evaluate [tex]\( f(-10) \)[/tex].

3. Substitute [tex]\( x = -10 \)[/tex] into the polynomial:
[tex]\[ f(-10) = (-10)^3 - 75(-10) + 250 \][/tex]

4. Perform the calculations step-by-step:
- Calculate [tex]\((-10)^3\)[/tex]:
[tex]\[ (-10)^3 = -1000 \][/tex]
- Calculate [tex]\(-75 \times (-10)\)[/tex]:
[tex]\[ -75 \times (-10) = 750 \][/tex]
- Now, sum these values including the constant 250:
[tex]\[ f(-10) = -1000 + 750 + 250 \][/tex]

5. Combine the results:
[tex]\[ -1000 + 750 + 250 = 0 \][/tex]

6. Conclusion:
Since [tex]\( f(-10) = 0 \)[/tex], by the Remainder Theorem, it indicates that [tex]\( x + 10 \)[/tex] is indeed a factor of the polynomial [tex]\( f(x) = x^3 - 75x + 250 \)[/tex].

Thus, we have shown that [tex]\( x + 10 \)[/tex] is a factor of the function [tex]\( f(x) = x^3 - 75x + 250 \)[/tex] because the remainder when [tex]\( f(x) \)[/tex] is divided by [tex]\( x + 10 \)[/tex] is zero.