How to find the equation of a line

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SSAT Upper Level Quantitative › How to find the equation of a line

Questions 1 - 10
1

Let y = 3_x_ – 6.

At what point does the line above intersect the following:

They do not intersect

They intersect at all points

(0,–1)

(–5,6)

(–3,–3)

Explanation

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

2

Find the equation of the line that has a slope of and passes through the point .

Explanation

In finding the equation of the line given its slope and a point through which it passes, we can use the slope-intercept form of the equation of a line:

, where is the slope of the line and is its -intercept.

Since the problem gives us the slope of the line , we just need to use the point that is given to us to find the -intercept. Plug in known values for and taken from the given point into the equation and solve for to find the -intercept:

Multiply:

Add to each side of the equation:

Now, we can write the final equation by plugging in the given slope and the -intercept :

3

Find the equation of the line that has a slope of and passes through the point .

Explanation

In finding the equation of the line given its slope and a point through which it passes, we can use the slope-intercept form of the equation of a line:

, where is the slope of the line and is its -intercept.

Since the problem gives us the slope of the line , we just need to use the point that is given to us to find the -intercept. Plug in known values for and taken from the given point into the equation and solve for to find the -intercept:

Multiply:

Subtract from each side of the equation:

Now, we can write the final equation by plugging in the given slope and the -intercept :

4

Find the equation of a line that has a slope of and passes through the point .

Explanation

The question gives us both the slope and the -intercept of the line. Remember that represents the slope, and represents the -intercept to write the following equation:

Alternatively, if you did not realize that the problem gives you the -intercept, you could solve it by using the slope-intercept form of the equation of a line:

, where is the slope of the line and is its -intercept.

Since the problem gives us the slope of the line , we would just need to use the point that is given to us to find the -intercept. We could plug in the known values for and taken from the given point into the equation and solve for to find the -intercept:

Multiplying leaves us with:

.

We could then substitute in the given slope and the -intercept into the equation to arrive at the correct answer:

5

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

3x + 5y = 2

2x – 3y = 5

4x – 5y = 4

–3x + 2y = 3

–2x + 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.

6

Find the equation of the line that has a slope of and passes through the point .

Explanation

The question gives us both the slope and the -intercept of the line, allowing us to write the following equation by inserting those values into the slope-intercept form of the equation of a line, :

Alternatively, if you did not realize that the problem gives you the -intercept, you could solve it by using the slope-intercept form of the equation of a line. Since the problem gives us the slope of the line , we would just need to use the point that is given to us to find the -intercept. We could plug in the known values for and taken from the given point into the equation and solve for to find the -intercept:

Multiplying leaves us with:

We could then substitute in the given slope and the -intercept into the equation to arrive at the correct answer:

7

Find the equation of the line that passes through the points and .

Explanation

First, notice that our -intercept for this line is ; we can tell this because one of the points, , is on the -axis since it has a value of for .

Now, we need to find the slope of the line. We can do that by using the slope equation:

We can substitute in the values of the provided points—,, and —and then solve for the slope of the line that connects them:

Now, put the two pieces of information together and substitute them into the equation to solve the problem:

8

Find the equation of the line that passes through and .

Explanation

First, notice that our -intercept for this line is ; we can tell this because one of the points, , is on the -axis since it has a value of for .

Now, we need to find the slope of the line. We can do that by using the slope equation:

We can substitute in the values of the provided points—,, and —and then solve for the slope of the line that connects them:

Now, put the two pieces of information together and substitute them into the equation to solve the problem:

9

Find the equation of a line that has a slope of and passes through the points .

Explanation

In finding the equation of the line given its slope and a point through which it passes, we can use the slope-intercept form of the equation of a line:

, where is the slope of the line and is its -intercept.

Since the problem gives us the slope of the line , we just need to use the point that is given to us to find the -intercept. Plug in known values for and taken from the given point into the equation to find the -intercept:

Multiply:

Subtract from each side of the equation:

Now that you've solved for , you can plug the given slope and the -intercept into the slope-intercept form of the equation of a line to figure out the answer:

10

Find the equation of the line that passes through the points .

Explanation

First, notice that our -intercept for this line is ; we can tell this because one of the points, , is on the -axis since it has a value of for .

Now, we need to find the slope of the line. We can do that by using the slope equation:

We can substitute in the values of the provided points—,, and —and then solve for the slope of the line that connects them:

Now, put the two pieces of information together and substitute them into the equation to solve the problem:

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