A software designer is mapping the streets for a new racing game. All of the streets are depicted as either perpendicular or parallel lines. The equation of the lane passing through points A and B is [tex]\(-7x + 3y = -21.5\)[/tex]. What is the equation of the central street PQ?

A. [tex]\(-3x + 4y = 3\)[/tex]
B. [tex]\(3x + 7y = 63\)[/tex]
C. [tex]\(2x + y = 20\)[/tex]
D. [tex]\(7x + 3y = 70\)[/tex]



Answer :

To determine which of the given equations could represent the central street [tex]\(PQ\)[/tex] parallel or perpendicular to the street passing through points [tex]\(A\)[/tex] and [tex]\(B\)[/tex], we'll start by identifying the slope of the line given by [tex]\(-7x + 3y = -21.5\)[/tex].

First, let's rearrange the equation [tex]\(-7x + 3y = -21.5\)[/tex] into the slope-intercept form [tex]\(y = mx + b\)[/tex], where [tex]\(m\)[/tex] represents the slope:

[tex]\[ -7x + 3y = -21.5 \][/tex]

Add [tex]\(7x\)[/tex] to both sides:

[tex]\[ 3y = 7x - 21.5 \][/tex]

Divide both sides by [tex]\(3\)[/tex]:

[tex]\[ y = \frac{7}{3}x - \frac{21.5}{3} \][/tex]

From this, we observe that the slope [tex]\(m\)[/tex] of the line passing through points [tex]\(A\)[/tex] and [tex]\(B\)[/tex] is [tex]\(\frac{7}{3}\)[/tex].

Next, we'll analyze the slopes of the equations provided in the options, and we aim to identify a line that's either parallel (same slope) or perpendicular (negative reciprocal slope) to the given line.

### Option A: [tex]\(-3x + 4y = 3\)[/tex]

Rearrange it into slope-intercept form:

[tex]\[ -3x + 4y = 3 \][/tex]

Add [tex]\(3x\)[/tex] to both sides:

[tex]\[ 4y = 3x + 3 \][/tex]

Divide both sides by [tex]\(4\)[/tex]:

[tex]\[ y = \frac{3}{4}x + \frac{3}{4} \][/tex]

The slope is [tex]\(\frac{3}{4}\)[/tex].

### Option B: [tex]\(3x + 7y = 63\)[/tex]

Rearrange it into slope-intercept form:

[tex]\[ 3x + 7y = 63 \][/tex]

Subtract [tex]\(3x\)[/tex] from both sides:

[tex]\[ 7y = -3x + 63 \][/tex]

Divide both sides by [tex]\(7\)[/tex]:

[tex]\[ y = -\frac{3}{7}x + 9 \][/tex]

The slope is [tex]\(-\frac{3}{7}\)[/tex].

### Option C: [tex]\(2x + y = 20\)[/tex]

Rearrange it into slope-intercept form:

[tex]\[ 2x + y = 20 \][/tex]

Subtract [tex]\(2x\)[/tex] from both sides:

[tex]\[ y = -2x + 20 \][/tex]

The slope is [tex]\(-2\)[/tex].

### Option D: [tex]\(7x + 3y = 70\)[/tex]

Rearrange it into slope-intercept form:

[tex]\[ 7x + 3y = 70 \][/tex]

Subtract [tex]\(7x\)[/tex] from both sides:

[tex]\[ 3y = -7x + 70 \][/tex]

Divide both sides by [tex]\(3\)[/tex]:

[tex]\[ y = -\frac{7}{3}x + \frac{70}{3} \][/tex]

The slope is [tex]\(-\frac{7}{3}\)[/tex].

Having identified the slopes of the given lines, we look for a line with either the same slope as [tex]\(\frac{7}{3}\)[/tex] (parallel) or the slope [tex]\(-\frac{3}{7}\)[/tex] (perpendicular).

Comparing:
- Option A: Slope [tex]\(\frac{3}{4}\)[/tex]
- Option B: Slope [tex]\(-\frac{3}{7}\)[/tex]
- Option C: Slope [tex]\(-2\)[/tex]
- Option D: Slope [tex]\(-\frac{7}{3}\)[/tex]

We see that the slope in option B [tex]\(-\frac{3}{7}\)[/tex] is the negative reciprocal of [tex]\(\frac{7}{3}\)[/tex] which indicates that it is perpendicular to the given line, fitting the problem's scenario.

Thus, the equation of the central street [tex]\(PQ\)[/tex] is:

[tex]\[ \boxed{3x + 7y = 63} \][/tex]

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