GRE Math : How to find the equation of a line

Study concepts, example questions & explanations for GRE Math

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Example Questions

Example Question #101 : Algebra

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

Possible Answers:

Correct answer:

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 #2 : 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=3x+2

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

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

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

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

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.

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

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

This is our final answer.

Example Question #61 : Geometry

Which of the following equations does NOT represent a line?

Possible Answers:

Correct answer:

Explanation:

The answer is .

A line can only be represented in the form  or , for appropriate constants , , and . A graph must have an equation that can be put into one of these forms to be a line.

 represents a parabola, not a line. Lines will never contain an term.

Example Question #143 : Coordinate Geometry

Let y = 3x – 6.

At what point does the line above intersect the following:

 

 

Possible Answers:

They do not intersect

(–5,6)

They intersect at all points

(0,–1)

(–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.

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