GRE Math : Coordinate Geometry

Study concepts, example questions & explanations for GRE Math

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Example Questions

Example Question #2 : How To Find The Endpoints Of A Line Segment

There is a line defined by two end-points,  and .  The midpoint between these two points is .  What is the value of the point ?

Possible Answers:

Correct answer:

Explanation:

Recall that to find the midpoint of two points  and , you use the equation:

.

(It is just like finding the average of the two points, really.)

So, for our equation, we know the following:

You merely need to solve each coordinate for its respective value.

Then, for the y-coordinate:

Therefore, our other point is: 

Example Question #3 : How To Find The Endpoints Of A Line Segment

What is the other endpoint of a line segment with one point that is  and a midpoint of ?

Possible Answers:

Correct answer:

Explanation:

Recall that the midpoint formula is like finding the average of the  and  values for two points.  For two points  and , it is:

For our points, we are looking for .  We know:

We can solve for each of these coordinates separately:

X-Coordinate

Y-Coordinate:

Therefore, our point is 

Example Question #1 : How To Find The Endpoints Of A Line Segment

What is the other endpoint of a line segment with one point that is  and a midpoint of ?

Possible Answers:

Correct answer:

Explanation:

What is the other endpoint of a line segment with one point that is  and a midpoint of ?

Recall that the midpoint formula is like finding the average of the  and  values for two points.  For two points  and , it is:

For our points, we are looking for .  We know:

We can solve for each of these coordinates separately:

X-Coordinate

Y-Coordinate:

Therefore, our point is 

Example Question #1 : Midpoint Formula

What is the midpoint of (2, 5) and (14, 18)?

Possible Answers:

(7, 9)

(16, 23)

(–10, –13)

(1, 2.5)

(8, 11.5)

Correct answer:

(8, 11.5)

Explanation:

The midpoint between two given points is found by solving for the average of each of the correlative coordinates of the given points.  That is:

Midpoint = ( (2 + 14)/2 , (18 + 5)/2) = (16/2, 23/2) = (8, 11.5)

Example Question #2 : How To Find The Midpoint Of A Line Segment

What is the midpoint between the points (1,3,7) and (–3,1,3)?

Possible Answers:

(3,1,2)

(2,–1,5)

(2,2,5)

(–1,2,5)

(5,2,4)

Correct answer:

(–1,2,5)

Explanation:

To find the midpoint, we add up the corresponding coordinates and divide by 2.  

[1 + –3] / 2 = –1

[3 + 1] / 2 = 2

[7 + 3] / 2 = 5

Then the midpoint is (–1,2,5).

Example Question #1 : How To Find The Midpoint Of A Line Segment

A line which cuts another line segment into two equal parts is called a ___________.

Possible Answers:

horizontal line

parallel line

bisector

midpoint

transversal

Correct answer:

bisector

Explanation:

This is the definition of a bisector. 

A midpoint is the point on a line that divides it into two equal parts. The bisector cuts the line at the midpoint, but the midpoint is not a line.

A transversal is a line that cuts across two or more lines that are usually parallel. 

Parallel line and horizontal line don't make sense as answer choices here. The answer is bisector.

Example Question #1 : How To Find Out If Lines Are Perpendicular

what would be the slope of a line perpendicular to

4x+3y = 6

Possible Answers:

4

4/3

-4/3

-3/4

3/4

Correct answer:

3/4

Explanation:

switch 4x+ 3y = 6 to "y=mx+b" form

 

3y= -4x + 6

y = -4/3 x + 2

m = -4/3; the perpendicular line will have the negative reciprocal of this line so it would be 3/4

Example Question #1 : How To Find Out If Lines Are Perpendicular

Which line is perpendicular to the line between the points (22,24) and (31,4)?

Possible Answers:

y = .45x + 10

the line between the points (4, 7) and (7, 4)

y = x

y = –3x + 5

the line between the points (9, 5) and (48, 19)

Correct answer:

y = .45x + 10

Explanation:

The line will be perpendicular if the slope is the negative reciprocal.

First we need to find the slope of our line between points (22,24) and (31,4). Slope = rise/run = (24 – 4)/(22 – 31) = 20/–9 = –2.22.

The negative reciprocal of this must be a positive fraction, so we can eliminate y = –3+ 5 (because the slope is negative).

The negative reciprocal of –2.22, and therefore the slope of the perpendicular line, will be –1/–2.22 = .45, so we can also eliminate y = x (slope of 1).

Now let's look at the line between points (9, 5) and (48, 19). This slope = (5 – 19)/(9 – 48) = .358, which is incorrect.

The next answer choice is y = .45x + 10. The slope is .45, which is what we're looking for so this is the correct answer.

To double check, the last answer choice is the line between (4, 7) and (7, 4). This slope = (7 – 4) / (4 – 7) = –1, which is also incorrect.

Example Question #3 : How To Find Out If Lines Are Perpendicular

Which best describes the relationship between the lines y = \frac{3}{4}x + 8  and y = \frac{-4}{3}x + 6 ?

Possible Answers:

The equations describe the same line.

The lines are parallel.

The lines are perpendicular.

None of the above.

Correct answer:

The lines are perpendicular.

Explanation:

We first need to recall the following relationships:

Lines with the same slope and same \dpi{100} \small y-intercept are really the same line.

Lines with the same slope and different \dpi{100} \small y-intercepts are parallel.

Lines with slopes that are negative reciprocals are perpendicular.

Then we identify the slopes of the two lines by comparing the equations to the slope-intercept form \dpi{100} \small y=mx+b, where \dpi{100} \small m is the slope and \dpi{100} \small b is the \dpi{100} \small y-intercept. By inspection we see the lines have slopes of \dpi{100} \small \frac{3}{4} and \dpi{100} \small \frac{-4}{3}. Since these are different, the "parallel" and "same line" choices are eliminated. To test if the slopes are negative reciprocals, we take one of the slopes, change its sign, and flip it upside-down. Starting with \dpi{100} \small \frac{3}{4} and changing the sign gives \dpi{100} \small \frac{-3}{4}, then flipping gives \dpi{100} \small \frac{-4}{3}. This is the same as the slope of the second line, so the two slopes are negative reciprocals and the lines are perpendicular.

Example Question #4 : How To Find Out If Lines Are Perpendicular

Which of the following lines is perpendicular to the line defined as ?

Possible Answers:

Correct answer:

Explanation:

To begin, the best thing to do is to put your equation into slope-intercept format. That is, into the format:

For your equation, you need to solve for :

, which is the same as 

Then, divide both sides by :

So, the slope of this line is .  The perpendicular of a line is opposite and reciprocal. Therefore, the perpendicular line will have a slope of . Of the options given, only  matches this (which you can figure out when you solve for ).

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