Select the correct answer.

[tex]\overleftrightarrow{AB}[/tex] and [tex]\overleftrightarrow{BC}[/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{BC}[/tex]?

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



Answer :

To determine the equation of the line \(\overleftrightarrow{BC}\) which forms a right angle with the line \(\overleftrightarrow{AB}\) at point \(B\), we can follow these steps:

1. Calculate the slope of \(\overleftrightarrow{AB}\):
Given points \(A(-3, -1)\) and \(B(4, 4)\), the slope \(m_{AB}\) is calculated as:
[tex]\[ m_{AB} = \frac{4 - (-1)}{4 - (-3)} = \frac{4 + 1}{4 + 3} = \frac{5}{7} \][/tex]

2. Find the slope of \(\overleftrightarrow{BC}\):
Since \(\overleftrightarrow{BC}\) forms a right angle with \(\overleftrightarrow{AB}\), the slope \(m_{BC}\) is the negative reciprocal of \(m_{AB}\):
[tex]\[ m_{BC} = -\frac{1}{m_{AB}} = -\frac{1}{\frac{5}{7}} = -\frac{7}{5} \][/tex]

3. Write the equation of the line \(\overleftrightarrow{BC}\) in slope-intercept form:
Using point \(B(4, 4)\) and the slope \(m_{BC} = -\frac{7}{5}\), we use the point-slope form equation \(y - y_1 = m(x - x_1)\):
[tex]\[ y - 4 = -\frac{7}{5}(x - 4) \][/tex]
Distributing the slope and simplifying:
[tex]\[ y - 4 = -\frac{7}{5}x + \frac{28}{5} \][/tex]
[tex]\[ y = -\frac{7}{5}x + \frac{28}{5} + 4 \][/tex]
Converting 4 into a fraction with denominator 5:
[tex]\[ y = -\frac{7}{5}x + \frac{28}{5} + \frac{20}{5} \][/tex]
[tex]\[ y = -\frac{7}{5}x + \frac{48}{5} \][/tex]

4. Convert to standard form \(Ax + By = C\):
To eliminate the fractions, multiply every term by 5:
[tex]\[ 5y = -7x + 48 \][/tex]
[tex]\[ 7x + 5y = 48 \][/tex]

Now compare the converted equation \(7x + 5y = 48\) with the given options:

A. \( x + 3y = 16 \)

B. \( 2x + y = 12 \)

C. \(-7x - 5y = -48 \)

D. \(7x - 5y = 48 \)

The correct equation that matches is:
[tex]\[ \boxed{7x - 5y = 48} \][/tex]
Option D is the correct answer.

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