Given the values of the linear functions [tex]\( f(x) \)[/tex] and [tex]\( g(x) \)[/tex] in the tables, where is [tex]\( (f-g)(x) \)[/tex] positive?

\begin{tabular}{|c|c|c|c|c|c|}
\hline
[tex]$x$[/tex] & -10 & -7 & -4 & -1 & 2 \\
\hline
[tex]$f(x)$[/tex] & -3 & 6 & 15 & 24 & 33 \\
\hline
[tex]$g(x)$[/tex] & 9 & 6 & 3 & 0 & -3 \\
\hline
\end{tabular}

A. [tex]$(-\infty,-10)$[/tex]

B. [tex]$(-\infty,-7)$[/tex]

C. [tex]$(-7, \infty)$[/tex]

D. [tex]$(-10, \infty)$[/tex]



Answer :

To determine where [tex]\((f-g)(x)\)[/tex] is positive, we'll follow these steps:

1. Identify the values given:
- The [tex]\(x\)[/tex]-values are: [tex]\(-10, -7, -4, -1, 2\)[/tex]
- The corresponding values of [tex]\(f(x)\)[/tex] are: [tex]\(-3, 6, 15, 24, 33\)[/tex]
- The corresponding values of [tex]\(g(x)\)[/tex] are: [tex]\(9, 6, 3, 0, -3\)[/tex]

2. Calculate [tex]\((f-g)(x)\)[/tex]:
- At [tex]\(x = -10\)[/tex]: [tex]\(f(-10) - g(-10) = -3 - 9 = -12\)[/tex]
- At [tex]\(x = -7\)[/tex]: [tex]\(f(-7) - g(-7) = 6 - 6 = 0\)[/tex]
- At [tex]\(x = -4\)[/tex]: [tex]\(f(-4) - g(-4) = 15 - 3 = 12\)[/tex]
- At [tex]\(x = -1\)[/tex]: [tex]\(f(-1) - g(-1) = 24 - 0 = 24\)[/tex]
- At [tex]\(x = 2\)[/tex]: [tex]\(f(2) - g(2) = 33 - (-3) = 36\)[/tex]

So, the differences [tex]\((f-g)(x)\)[/tex] are:
- At [tex]\(x = -10\)[/tex]: [tex]\(-12\)[/tex]
- At [tex]\(x = -7\)[/tex]: [tex]\(0\)[/tex]
- At [tex]\(x = -4\)[/tex]: [tex]\(12\)[/tex]
- At [tex]\(x = -1\)[/tex]: [tex]\(24\)[/tex]
- At [tex]\(x = 2\)[/tex]: [tex]\(36\)[/tex]

3. Determine where [tex]\((f-g)(x)\)[/tex] is positive:
- We can see from the calculations that [tex]\((f-g)(x)\)[/tex] is positive at [tex]\(x = -4, -1,\text{ and } 2\)[/tex].

4. Find the range of [tex]\(x\)[/tex] values where [tex]\((f-g)(x)\)[/tex] is positive:
- For [tex]\((f-g)(x)\)[/tex] to be consistently positive, we observe the smallest [tex]\(x\)[/tex] value where it turns positive is [tex]\(-4\)[/tex] and it remains positive for all subsequent [tex]\(x\)[/tex] values.
- Since [tex]\((f-g)(x)\)[/tex] is zero at [tex]\(x = -7\)[/tex] and negative at [tex]\(x = -10\)[/tex], the positive interval must start just after [tex]\(-7\)[/tex].

Therefore, the interval where [tex]\((f-g)(x)\)[/tex] is positive is [tex]\((-7, \infty)\)[/tex].