GRE Math : Lines

Study concepts, example questions & explanations for GRE Math

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Example Questions

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

Given the graph of the line below, find the equation of the line.

 

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Possible Answers:

\displaystyle y=x-4

\displaystyle y=-5x-4

\displaystyle y=\frac{10}{3}x-4

\displaystyle y=-x

Correct answer:

\displaystyle y=\frac{10}{3}x-4

Explanation:

To solve this question, you could use two points such as (1.2,0) and (0,-4) to calculate the slope which is 10/3 and then read the y-intercept off the graph, which is -4.

 

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

Which line passes through the points (0, 6) and (4, 0)?

Possible Answers:

y = –3/2x + 6

y = 2/3 + 5

y = 1/5x + 3

y = 2/3x –6

y = –3/2 – 3

Correct answer:

y = –3/2x + 6

Explanation:

P1 (0, 6) and P2 (4, 0)

First, calculate the slope:  m = rise ÷ run = (y2 – y1)/(x– x1), so m = –3/2

Second, plug the slope and one point into the slope-intercept formula: 

y = mx + b, so 0 = –3/2(4) + b and b = 6

Thus, y = –3/2x + 6

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

What line goes through the points (1, 3) and (3, 6)?

Possible Answers:

–3x + 2y = 3

3x + 5y = 2

2x – 3y = 5

–2x + 2y = 3

4x – 5y = 4

Correct answer:

–3x + 2y = 3

Explanation:

If P1(1, 3) and P2(3, 6), then calculate the slope by m = rise/run = (y2 – y1)/(x2 – x1) = 3/2

Use the slope and one point to calculate the intercept using y = mx + b

Then convert the slope-intercept form into standard form.

Example Question #531 : Sat Mathematics

What is the slope-intercept form of \dpi{100} \small 8x-2y-12=0?

Possible Answers:

\dpi{100} \small y=4x+6

\dpi{100} \small y=2x-3

\dpi{100} \small y=-4x+6

\dpi{100} \small y=4x-6

\dpi{100} \small y=-2x+3

Correct answer:

\dpi{100} \small y=4x-6

Explanation:

The slope intercept form states that \dpi{100} \small y=mx+b. In order to convert the equation to the slope intercept form, isolate \dpi{100} \small y on the left side:

\dpi{100} \small 8x-2y=12

\dpi{100} \small -2y=-8x+12

\dpi{100} \small y=4x-6

Example Question #5 : How To Find The Equation Of A Line

A line is defined by the following equation:

\displaystyle 7x+28y=84

What is the slope of that line?

Possible Answers:

\displaystyle 28

\displaystyle 4

\displaystyle -4

\displaystyle \frac{1}{4}

\displaystyle -\frac{1}{4}

Correct answer:

\displaystyle -\frac{1}{4}

Explanation:

The equation of a line is

y=mx + b where m is the slope

Rearrange the equation to match this:

7x + 28y = 84

28y = -7x + 84

y = -(7/28)x + 84/28

y = -(1/4)x + 3

m = -1/4

Example Question #532 : Sat Mathematics

If the coordinates (3, 14) and (5, 15) are on the same line, what is the equation of the line?

Possible Answers:

\displaystyle y=\frac{1}{8}x+14.375

\displaystyle y=-\frac{1}{8}x+14.375

\displaystyle y=-\frac{1}{8}x+13.625

\displaystyle y=-8x-38

\displaystyle y=-8x+38

Correct answer:

\displaystyle y=-\frac{1}{8}x+14.375

Explanation:

First solve for the slope of the line, m using y=mx+b

m = (y2 – y1) / (x2 – x1)

= (15  14) / (5 3)

= (1 )/( 8)

=1/8

y = (1/8)x + b

Now, choose one of the coordinates and solve for b:

14 = (1/8)3 + b

14 = 3/8 + b

b = 14 + (3/8)

b = 14.375

y = (1/8)x + 14.375

Example Question #1 : Coordinate Geometry

What is the equation of a line that passes through coordinates \dpi{100} \small (2,6) and \dpi{100} \small (3,5)?

Possible Answers:

\dpi{100} \small y=2x+4

\dpi{100} \small y=3x+2

\dpi{100} \small y=x+7

\dpi{100} \small y=-x+8

\dpi{100} \small y=2x-4

Correct answer:

\dpi{100} \small y=-x+8

Explanation:

Our first step will be to determing the slope of the line that connects the given points.

\displaystyle m=\frac{y_2-y_1}{x_2-x_1}=\frac{6-5}{2-3}=\frac{1}{-1}=-1

Our slope will be \displaystyle -1. Using slope-intercept form, our equation will be \displaystyle y=(-1)x+b. Use one of the give points in this equation to solve for the y-intercept. We will use \dpi{100} \small (2,6).

\displaystyle 6=(-1)(2)+b

\displaystyle 6=-2+b

\displaystyle 8=b

Now that we know the y-intercept, we can plug it back into the slope-intercept formula with the slope that we found earlier.

\displaystyle y=(-1)x+8

\displaystyle y=-x+8

This is our final answer.

Example Question #11 : How To Find The Equation Of A Line

Which of the following equations does NOT represent a line?

Possible Answers:

\displaystyle x=10

\displaystyle 5y=10

\displaystyle x-y=10

\displaystyle x+y=10

\displaystyle x^2+y=10

Correct answer:

\displaystyle x^2+y=10

Explanation:

The answer is \displaystyle x^2+y=10.

A line can only be represented in the form \displaystyle x=z or \displaystyle y=mx+b, for appropriate constants \displaystyle z, \displaystyle m, and \displaystyle b. A graph must have an equation that can be put into one of these forms to be a line.

\displaystyle x^2+y=10 represents a parabola, not a line. Lines will never contain an \displaystyle x^2 term.

Example Question #14 : How To Find The Equation Of A Line

Let y = 3x – 6.

At what point does the line above intersect the following:

\displaystyle 2x =\frac{2}{3}y+4

 

 

Possible Answers:

(0,–1)

They intersect at all points

(–5,6)

They do not intersect

(–3,–3)

Correct answer:

They intersect at all points

Explanation:

If we rearrange the second equation it is the same as the first equation. They are the same line.

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

There is a line defined by two end-points, \displaystyle (4,3) and \displaystyle (a,b).  The midpoint between these two points is \displaystyle (7,15).  What is the value of the point \displaystyle (a,b)?

Possible Answers:

\displaystyle (3,12)

\displaystyle (14,-1)

\displaystyle (12,3)

\displaystyle (13,41)

\displaystyle (10,27)

Correct answer:

\displaystyle (10,27)

Explanation:

Recall that to find the midpoint of two points \displaystyle (a,b) and \displaystyle (c,d), you use the equation:

\displaystyle \left(\frac{a+c}{2},\frac{b+d}{2}\right).

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

So, for our equation, we know the following:

\displaystyle \left(\frac{4+a}{2},\frac{3+b}{2}\right)=(7,15)

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

\displaystyle \frac{4+a}{2}=7

\displaystyle 4+a=14

\displaystyle a=10

Then, for the y-coordinate:

\displaystyle \frac{3+b}{2}=15

\displaystyle 3+b=30

\displaystyle b=27

Therefore, our other point is: \displaystyle (10,27)

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