Pretest: Coordinate Geometry

Type the correct answer in each box. Use numerals instead of words. If necessary, use / for the fraction bar.

[tex]$\stackrel{\rightharpoonup B}{\longleftrightarrow}$[/tex] and [tex]$\stackrel{B C}{\longleftrightarrow}$[/tex] form a right angle at their point of intersection, [tex]$B$[/tex].

If the coordinates of [tex]$A$[/tex] and [tex]$B$[/tex] are [tex]$(14,-1)$[/tex] and [tex]$(2,1)$[/tex], respectively, the [tex]$y$[/tex]-intercept of [tex]$\overleftrightarrow{A B}$[/tex] is [tex]$y = \square x + \square$[/tex].

If the [tex]$y$[/tex]-coordinate of point [tex]$C$[/tex] is 13, its [tex]$x$[/tex]-coordinate is [tex]$\square$[/tex].



Answer :

Let's solve the problem step-by-step.

1. Find the equation of the line [tex]\( \overleftrightarrow{AB} \)[/tex]:
- The coordinates of points [tex]\( A \)[/tex] and [tex]\( B \)[/tex] are given as [tex]\( A(14, -1) \)[/tex] and [tex]\( B(2, 1) \)[/tex].
- First, let's calculate the slope [tex]\( m \)[/tex] of the line [tex]\( \overleftrightarrow{AB} \)[/tex]:
[tex]\[ m = \frac{y_2 - y_1}{x_2 - x_1} = \frac{1 - (-1)}{2 - 14} = \frac{2}{-12} = -\frac{1}{6} \][/tex]
- Next, we find the y-intercept [tex]\( b \)[/tex] of the line using the point-slope form of the equation [tex]\( y = mx + b \)[/tex]. Plugging in the coordinates of point [tex]\( B(2, 1) \)[/tex]:
[tex]\[ 1 = -\frac{1}{6} \cdot 2 + b \implies 1 = -\frac{1}{3} + b \implies b = 1 + \frac{1}{3} = \frac{3}{3} + \frac{1}{3} = \frac{4}{3} \approx 1.33 \][/tex]

- Therefore, the equation of the line [tex]\( \overleftrightarrow{AB} \)[/tex] in the form [tex]\( y = mx + b \)[/tex] is:
[tex]\[ y = -\frac{1}{6}x + \frac{4}{3} \][/tex]

2. Determine the coordinates of point [tex]\( C \)[/tex]:
- The y-coordinate of point [tex]\( C \)[/tex] is given as [tex]\( y_C = 13 \)[/tex].
- Since [tex]\( \overleftrightarrow{BC} \)[/tex] is perpendicular to [tex]\( \overleftrightarrow{AB} \)[/tex], the slope of [tex]\( \overleftrightarrow{BC} \)[/tex] is the negative reciprocal of the slope of [tex]\( \overleftrightarrow{AB} \)[/tex]. Thus, the slope of [tex]\( \overleftrightarrow{BC} \)[/tex] is:
[tex]\[ m_{BC} = -\left(-1 \div \frac{1}{6}\right) = 6 \][/tex]

- To find [tex]\( x_C \)[/tex], we will use the point-slope form and convert it to the slope-intercept form of [tex]\( \overleftrightarrow{BC} \)[/tex] passing through point [tex]\( B(2, 1) \)[/tex]:
[tex]\[ y - 1 = 6(x - 2) \][/tex]
Simplifying for [tex]\( y \)[/tex]:
[tex]\[ y = 6x - 12 + 1 \implies y = 6x - 11 \][/tex]
Now, solve for [tex]\( x \)[/tex] when [tex]\( y_C = 13 \)[/tex]:
[tex]\[ 13 = 6x - 11 \implies 13 + 11 = 6x \implies 24 = 6x \implies x = 4 \][/tex]

Thus, summarizing the solutions:

1. The equation of the line [tex]\( \overleftrightarrow{AB} \)[/tex] is:
[tex]\[ y = -\frac{1}{6} x + \frac{4}{3} \][/tex]

2. The x-coordinate of point [tex]\( C \)[/tex] for [tex]\( y_C = 13 \)[/tex] is:
[tex]\[ x = 4 \][/tex]