How to find the equation of a line

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

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1

Let y = 3_x_ – 6.

At what point does the line above intersect the following:

They do not intersect

0

They intersect at all points

CORRECT

(0,–1)

0

(–5,6)

0

(–3,–3)

0

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 .

CORRECT

0

0

0

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 .

CORRECT

0

0

0

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 .

CORRECT

0

0

0

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

0

2x – 3y = 5

0

4x – 5y = 4

0

–3x + 2y = 3

CORRECT

–2x + 2y = 3

0

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 .

CORRECT

0

0

0

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 .

CORRECT

0

0

0

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 .

CORRECT

0

0

0

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 .

CORRECT

0

0

0

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 .

CORRECT

0

0

0

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: