Algebra 1 : How to find the equation of a line

Study concepts, example questions & explanations for Algebra 1

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Example Questions

Example Question #11 : Slope And Line Equations

Which of these lines has a slope of  and a -intercept of ?

Possible Answers:

None of the other answers

Correct answer:

Explanation:

When a line is in the form, the is its slope and the is its -intercept. Thus, the only line with a slope of and a -intercept of is

.

Example Question #12 : Slope And Line Equations

What is the equation of a line with a slope of 3 that runs through the point (4,9)?

Possible Answers:

None of the other answers

Correct answer:

Explanation:

You can find the equation by plugging in all of the information to the formula.

The slope (or ) is 3. So, the equation is now .

You are also given a point on the line: (4,9), which you can plug into the equation:

Solve for to get .

Now that you have the and , you can determine that the equation of the line is .

Example Question #13 : Slope And Line Equations

What is the equation of the line passing through the points (1,2) and (3,1) ?

Possible Answers:

Correct answer:

Explanation:

First find the slope of the 2 points:

Then use the slope and one of the points to find the y-intercept:

So the final equation is 

Example Question #14 : Slope And Line Equations

What is the slope and y-intercept of ?

Possible Answers:

None of the other answers

Slope: ; y-intercept:

Slope: ; y-intercept:

Slope: ; y-intercept:

Slope: ; y-intercept:

Correct answer:

Slope: ; y-intercept:

Explanation:

The easiest way to determine the slope and y-intercept of a line is by rearranging its equation to the form. In this form, the slope is the  and the y-intercept is the .

Rearranging

gives you

which has an of 2 and a of 6.

Example Question #15 : Slope And Line Equations

Find the equation of the line, in  form, that contains the points , , and .

Possible Answers:

Correct answer:

Explanation:

When finding the equation of a line given two or more points, the first step is to find the slope of that line. We can use the slope equation, . Any combination of the three points can be used, but let's consider the first two points,  and .

 

So  is our slope.

Now, we have the half-finished equation

 

and we can complete it by plugging in the  and  values of any point. Let's use .

Solving

  

for  gives us

 

so

 

We now have our completed equation: 

Example Question #16 : Slope And Line Equations

We have two points:  and .

If these two points are connected by a straight line, find the equation describing this straight line.

Possible Answers:

None of these

Correct answer:

Explanation:

We need to find the equation of the line in slope-intercept form.

In this formula, is equal to the slope and is equal to the y-intercept.

To find this equation, first, we need to find the slope by using the formula for the slope between two point.

In the formula, the points are  and .  In our case, the points are  and . Using our values allows us to solve for the slope.

We can replace the variable with our new slope.

Next, we need to find the y-intercept. To find this intercept, we can pick one of our given points and use it in the formula.

Solve for .

Now, the final equation connecting the two points can be written using the new value for the y-intercept.

Example Question #17 : Slope And Line Equations

Which of these lines has a slope of  and a y-intercept of ?

Possible Answers:

None of the other answers

Correct answer:

Explanation:

Since all of the answers are in the  form, the slope of each line is indicated by its  and its y-intercept is indicated by its . Thus, a line with a slope of  and a y-intercept of  must have an equation of .

Example Question #18 : Slope And Line Equations

Find the domain of:

 

Possible Answers:

Correct answer:

Explanation:

The expression under the radical must be .  Hence

 

Solving for , we get

Example Question #19 : Slope And Line Equations

Give, in slope-intercept form, the equation of a line through the points  and .

Possible Answers:

Correct answer:

Explanation:

First, use the slope formula to find the slope, setting .

We can write the equation in slope-intercept form as

.

Replace :

We can find  by substituting for  using either point - we will choose :

The equation is .

Example Question #20 : Slope And Line Equations

Give, in slope-intercept form, the equation of a line through the points  and .

Possible Answers:

Correct answer:

Explanation:

First, use the slope formula to find the slope, setting .

We can write the equation in slope-intercept form as

.

Replace :

We can find  by substituting for  using either point - we will choose :

The equation is .

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