PSAT Math : How to find the equation of a parallel line

Study concepts, example questions & explanations for PSAT Math

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Example Questions

Example Question #1 : How To Find The Equation Of A Parallel Line

Which of the following is the equation of a line that is parallel to the line 4x – y = 22 and passes through the origin?

Possible Answers:

y – 4x = 22

4x + 8y = 0

(1/4)x + y = 0

4x = 8y

4x – y = 0

Correct answer:

4x – y = 0

Explanation:

We start by rearranging the equation into the form y = mx + b (where m is the slope and b is the y intercept); y = 4x – 22
Now we know the slope is 4 and so the equation we are looking for must have the m = 4 because the lines are parallel. We are also told that the equation must pass through the origin; this means that b = 0.

In 4x – y = 0 we can rearrange to get y = 4x. This fulfills both requirements.

Example Question #2 : How To Find The Equation Of A Parallel Line

What line is parallel to 2x + 5y = 6 through (5, 3)?

Possible Answers:

y = –2/5x + 5

y = –2/3x + 3

y = 3/5x – 2

y = 5/3x – 5

y = 5/2x + 3

Correct answer:

y = –2/5x + 5

Explanation:

The given equation is in standard form and needs to be converted to slope-intercept form which gives y = –2/5x + 6/5. The parallel line will have a slope of –2/5 (the same slope as the old line). The slope and the given point are substituted back into the slope-intercept form to yield y = –2/5x +5.

Example Question #3 : Parallel Lines

What line is parallel to  through ?

Possible Answers:

Correct answer:

Explanation:

The slope of the given line is  and a parallel line would have the same slope, so we need to find a line through  with a slope of 2 by using the slope-intercept form of the equation for a line.  The resulting line is  which needs to be converted to the standard form to get .

Example Question #111 : Lines

Find the equation of a line parallel to  that also passes through the point .

Possible Answers:

Correct answer:

Explanation:

Since they are parallel, the line will have the same slope as .

 Thus, it will take the form .

We then use the point (3,2) to solve for :

so the equation of the line is

Example Question #112 : Lines

In the -plane, the line  is parallel to the line . What is the value of ?

Possible Answers:

Correct answer:

Explanation:

In this equation,  is equal to the slope of the line.  You have been given a line parallel to the line containing variable , and since parallel lines have the same slope, all you need to do is figure out the slope of  in order to figure out what  is.  To figure out the slope of , you need to convert the equation into  form, which means isolating  on one side of the equation.

 

Given this solution, the slope of the parallel lines, and thus , is equal to 2.

Example Question #1 : How To Find The Equation Of A Parallel Line

Which of the following lines has zero points of intersection with the line, ?

Possible Answers:

Correct answer:

Explanation:

This prompt asks you to find a line that is parallel to the one given. Parallel lines have no points of intersection (as opposed to intersecting lines which have 1 point of intersection). Parallel lines have the same slope, but different y-intercepts. If they had the same y-intercept, then they would actually be the same line. 

 

We can find the slope of the first line by converting it to slope-intercept form. 

 

First, subtract 3x from both sides.

 

Then, divide both sides by -2.

The slope of the line is 3/2. The only answer that has that same slope, but a different y-intercept is  .

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