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 #2 : How To Find The Equation Of A Line

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=-x+8

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

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

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

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

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 #21 : How To Find The Equation Of A Line

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 #7 : How To Find The Equation Of A Line

Let y = 3x – 6.

At what point does the line above intersect the following:

 

 

Possible Answers:

(–3,–3)

(–5,6)

They intersect at all points

(0,–1)

They do not intersect

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 #22 : How To Find The Equation Of A Line

Find the equation of a line that goes through the points , and .

Possible Answers:

Correct answer:

Explanation:

For finding the equation of a line, we will be using point-slope form, which is

, where  is the slope, and  is a point. 

We will pick the point 

If we picked the point 

 

We get the same result

Example Question #23 : How To Find The Equation Of A Line

Find the equation of a line that passes through the point , and is parallel to the line .

Possible Answers:

Correct answer:

Explanation:

Since we want a line that is parallel, we will have the same slope as the line . We can use point slope form to create an equation.

, where  is the slope and  is a point.

Example Question #24 : How To Find The Equation Of A Line

Find the equation of the line shown in the graph below:

 

 Sat_math_164_05

 
Possible Answers:

y = 2x + 4

y = -1/2x - 4

 y = -1/2x + 4

y = x/2 + 4

Correct answer:

y = x/2 + 4

Explanation:

Based on the graph the y-intercept is 4. So we can eliminate choice y = x/2 - 4.

The graph is rising to the right which means our slope is positive, so we can eliminate choice y = -1/2x + 4.

Based on the line, if we start at (0,4) and go up 1 then 2 to the right we will be back on the line, meaning we have a slope of  (1/2).

Using the slope intercept formula we can plug in y= (1/2)x + 4.

 

 

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