Parallel and Perpendicular Lines: Mastery Test

Select the correct answer.

[tex]$\overleftrightarrow{A B}$[/tex] and [tex]$\overleftrightarrow{B C}$[/tex] form a right angle at point [tex]$B$[/tex]. If [tex]$A=(-3,-1)$[/tex] and [tex]$B=(4,4)$[/tex], what is the equation of [tex]$\overleftrightarrow{B C}$[/tex]?

A. [tex]$x+3 y=16$[/tex]
B. [tex]$2 x+y=12$[/tex]
C. [tex]$-7 x-5 y=-48$[/tex]
D. [tex]$7 x-5 y=48$[/tex]



Answer :

To solve this problem, let's walk through the necessary steps:

1. Calculate the slope of line AB:

The coordinates of point [tex]\( A \)[/tex] are [tex]\((-3, -1)\)[/tex] and the coordinates of point [tex]\( B \)[/tex] are [tex]\( (4, 4) \)[/tex].

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]
Substituting the given points [tex]\( A \)[/tex] and [tex]\( B \)[/tex]:
[tex]\[ m_{AB} = \frac{4 - (-1)}{4 - (-3)} = \frac{4 + 1}{4 + 3} = \frac{5}{7} \][/tex]

2. Find the slope of line BC:

Since [tex]\(\overleftrightarrow{AB}\)[/tex] and [tex]\(\overleftrightarrow{BC}\)[/tex] form a right angle at [tex]\( B \)[/tex], the slope of line [tex]\( BC \)[/tex] will be the negative reciprocal of the slope of [tex]\( AB \)[/tex].

The negative reciprocal of [tex]\(\frac{5}{7}\)[/tex] is:
[tex]\[ m_{BC} = -\frac{7}{5} \][/tex]

3. Use the point-slope form to find the equation of line BC:

The point-slope form of the equation of a line is:
[tex]\[ y - y_1 = m(x - x_1) \][/tex]
Here, point [tex]\( B \)[/tex] is [tex]\((4, 4)\)[/tex] and the slope [tex]\( m \)[/tex] of [tex]\( BC \)[/tex] is [tex]\(-\frac{7}{5}\)[/tex]. Substituting these values in:
[tex]\[ y - 4 = -\frac{7}{5}(x - 4) \][/tex]

4. Rearrange to the standard form of the equation: Ax + By = C

First, distribute the slope on the right-hand side:
[tex]\[ y - 4 = -\frac{7}{5}x + \frac{28}{5} \][/tex]

Move all terms to one side to get the equation in standard form [tex]\(Ax + By = C\)[/tex]:
[tex]\[ y - 4 + \frac{7}{5}x = \frac{28}{5} \][/tex]

Multiply all terms by 5 to eliminate the fraction:
[tex]\[ 5y - 20 + 7x = 28 \][/tex]

Rearrange and combine like terms:
[tex]\[ 7x + 5y = 48 \][/tex]

To match the standard form [tex]\(Ax + By = C\)[/tex] with integer coefficients, the equation simplifies to:
[tex]\[ 7x - 5y = 48 \][/tex]

Given the choices:
- A. [tex]\( x + 3y = 16 \)[/tex]
- B. [tex]\( 2x + y = 12 \)[/tex]
- C. [tex]\( -7x - 5y = -48 \)[/tex]
- D. [tex]\( 7x - 5y = 48 \)[/tex]

The correct answer is:
D. [tex]\( 7x - 5y = 48 \)[/tex]