SAT Math : How to find the equation of a line

Study concepts, example questions & explanations for SAT Math

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Example Questions

Example Question #137 : Coordinate Geometry

 

Possible Answers:

Correct answer:

Explanation:

Equation of line: ,    = slope,  = -intercept

Step 1) Find slope ():  rise/run    

Step 2) Find -intercept ():    

                                                      

                                                      

                                                       

Example Question #138 : Coordinate Geometry

Whast line goes through the points  and ?

Possible Answers:

Correct answer:

Explanation:

Let P_{1}=(1,3) and P_{2}=(7,5)

The slope is geven by:  m = (y_{2} - y_{1}) \div (x_{2} - x_{1})  so

Then we use the slope-intercept form of an equation;   so

And we convert 

 

to standard form.

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

What is the equation of the line that passes through the points (4,7) and (8,10)?

Possible Answers:

Correct answer:

Explanation:

In order to find the equation of the line, we will first need to find the slope between the two points through which it passes. The slope, , of a line that passes through the points and is given by the formula below:

We are given our two points, (4,7) and (8,10), allowing us to calculate the slope.

Next, we can use point slope form to find the equation of a line with this slope that passes through one of the given points. We will use (4,7).

Multiply both sides by four to eliminate the fraction, and simplify by distribution.

Subtract from both sides and add twelve to both sides.

This gives our final answer:

Example Question #140 : Coordinate Geometry

Which line contains the following ordered pairs:

 and

Possible Answers:

\small y=\frac{1}{4}x+\frac{7}{2}

\small y=-x+14

\small y=x+14

\small y=-\frac{1}{4}x+\frac{7}{2}

Correct answer:

\small y=-\frac{1}{4}x+\frac{7}{2}

Explanation:

First, solve for slope.

\small m=\frac{\Delta y}{\Delta x}=\frac{2-4}{6-(-2)}=\frac{-2}{8}=-\frac{1}{4}

Then, substitute one of the points into the equation y=mx+b.

\small 2=(-\frac{1}{4})(6)+b

\small 2=(-\frac{3}{2})+b

\small b=2+\frac{3}{2}=\frac{7}{2}

This leaves us with the equation \small y=-\frac{1}{4}+\frac{7}{2}

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

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

 

Act_math_160_04

Possible Answers:

Correct answer:

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 #241 : Geometry

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

Possible Answers:

y = 1/5x + 3

y = 2/3x –6

y = –3/2 – 3

y = 2/3 + 5

y = –3/2x + 6

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 #1 : Coordinate Geometry

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

Possible Answers:

–2x + 2y = 3

4x – 5y = 4

–3x + 2y = 3

2x – 3y = 5

3x + 5y = 2

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 #144 : Coordinate Geometry

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

Possible Answers:

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

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

\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 #1 : Coordinate Geometry

A line is defined by the following equation:

What is the slope of that line?

Possible Answers:

Correct answer:

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 #1 : Lines

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

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