\begin{tabular}{|c|c|}
\hline
[tex]$x$[/tex] & [tex]$y$[/tex] \\
\hline
[tex]$k$[/tex] & 13 \\
\hline
[tex]$k+7$[/tex] & -15 \\
\hline
\end{tabular}

The table gives the coordinates of two points on a line in the [tex]$xy$[/tex]-plane. The [tex]$y$[/tex]-intercept of the line is [tex]$(0, b)$[/tex], where [tex]$k$[/tex] and [tex]$b$[/tex] are constants. What is the value of [tex]$b$[/tex]?



Answer :

To solve the problem, we need to determine the slope of the line, find the equation of the line in slope-intercept form, and then use this to find the [tex]\(y\)[/tex]-intercept when [tex]\(x = k-5\)[/tex].

Given points:
- Point 1: [tex]\((x_1, y_1) = (k, 13)\)[/tex]
- Point 2: [tex]\((x_2, y_2) = (k + 7, -15)\)[/tex]

### Step 1: Calculate the slope (m) of the line
The formula for the slope [tex]\(m\)[/tex] between two points [tex]\((x_1, y_1)\)[/tex] and [tex]\((x_2, y_2)\)[/tex] is:

[tex]\[ m = \frac{y_2 - y_1}{x_2 - x_1} \][/tex]

Substitute the given values:

[tex]\[ m = \frac{-15 - 13}{(k + 7) - k} = \frac{-28}{7} = -4 \][/tex]

The slope of the line is [tex]\(-4\)[/tex].

### Step 2: Write the equation of the line in point-slope form
The point-slope form of a line is:

[tex]\[ y - y_1 = m(x - x_1) \][/tex]

Using point 1 [tex]\((x_1, y_1) = (k, 13)\)[/tex] and the slope [tex]\(m = -4\)[/tex]:

[tex]\[ y - 13 = -4(x - k) \][/tex]

Simplify and rearrange to get the slope-intercept form [tex]\(y = mx + b\)[/tex]:

[tex]\[ y - 13 = -4x + 4k \][/tex]
[tex]\[ y = -4x + 4k + 13 \][/tex]

So, the equation of the line is:

[tex]\[ y = -4x + 4k + 13 \][/tex]

### Step 3: Find the [tex]\(y\)[/tex]-intercept for [tex]\(x = k - 5\)[/tex]
To find the value of [tex]\(b\)[/tex] when [tex]\(x = k-5\)[/tex]:

[tex]\[ y = -4(k - 5) + 4k + 13 \][/tex]

Simplify the expression:

[tex]\[ y = -4k + 20 + 4k + 13 \][/tex]
[tex]\[ y = 20 + 13 \][/tex]
[tex]\[ y = 33 \][/tex]

So, the [tex]\(y\)[/tex]-intercept of the line when [tex]\(x = k-5\)[/tex] is [tex]\(33\)[/tex].

Thus, the value of [tex]\(b\)[/tex] is [tex]\(\boxed{33}\)[/tex].

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