# GED Math : Parallel and Perpendicular Lines

## Example Questions

### Example Question #771 : Geometry And Graphs

Give ths slope of a line parallel to the line in the above figure.

Explanation:

In order to move from the lower left plotted point to the upper right plotted point, it is necessary to move up five units and right three units. This is a rise of 5 and a run of 3. The slope is the rise-to-run ratio, so the slope of the line is . Any line parallel to this line will have the same slope, so the correct response is .

### Example Question #772 : Geometry And Graphs

Give the slope of a line perpendicular to the line in the above figure.

Explanation:

In order to move from the lower left point to the upper right point, it is necessary to move up five units and right three units. This is a rise of 5 and a run of 3. The slope of a line is the ratio of rise to run, so the slope of the line shown is .

A line perpendicular to this will have a slope equal to the opposite of the reciprocal of . This is .

### Example Question #773 : Geometry And Graphs

Refer to the above red line. A line is drawn perpendicular to that line, and with the same -intercept. What is the equation of that line in slope-intercept form?

Explanation:

First, we need to find the slope of the above line.

The slope of a line. given two points  can be calculated using the slope formula:

Set :

The slope of a line perpendicular to it has as its slope the opposite of the reciprocal of 2, which would be .

Since we want the line to have the same -intercept as the above line, which is the point , we can use the slope-intercept form to help us.  We set

, and solve for :

Substitute for  and  in the slope-intercept form, and the equation is

.

### Example Question #774 : Geometry And Graphs

Which of the following equations is represented by a line perpendicular to the line  ?

Explanation:

The equation  can be rewritten as follows:

This is the slope-intercept form, and the line has slope

The line  therefore has slope . Since a line perpendicular to this one must have a slope that is the opposite reciprocal of , we are looking for a line that has slope .

The slopes of the lines in the four choices are as follows:

This is the correct choice.

### Example Question #781 : Geometry And Graphs

Given the following equation, what is the slope of the perpendicular line?

Explanation:

Subtract  from both sides.

The slope of this line is negative three.

The slope of the perpendicular line is the negative reciprocal of this slope.

### Example Question #782 : Geometry And Graphs

Which line is parallel to the following:

Explanation:

Two lines are parallel if they have the same slope. Now, we know the slope-intercept form is written as follows:

where m is the slope and b is the y-intercept. Now, given the equation

we can see the slope is -3. So, to find a line parallel to this line, we will have to find an equation that also have a slope of -3.

If we look at the equation

we can see it has a slope of -3. Therefore, this equation is parallel to the original equation.

### Example Question #783 : Geometry And Graphs

Find a line that is perpendicular to the following:

Explanation:

Two lines are perpendicular if their slopes have opposite signs (positive/negative) and they are reciprocals of each other.

To find a reciprocal of a number, we will write it in fraction form. Then, the numerator becomes the denominator and the denominator becomes the numerator. In other words, we flip the fraction.

We will look at the lines in slope-intercept form

where m is the slope and b is the y-intercept.

So, given the equation

we can see the slope is . Now, the opposite reciprocal of this slope is  which is the same as . So, we will find the equation that has  as the slope.

So, in the equation

we can see the slope is . Therefore, it is perpendicular to the original equation.

### Example Question #784 : Geometry And Graphs

Find a line that is parallel to the following line:

Explanation:

Two lines are parallel if they have the same slope. So, we will look at the lines in slope-intercept form:

where m is the slope and b is the y-intercept.

So, given the line

we can see the slope is -2. So, to find a line that is parallel, it must also have a slope of -2. So, the line

we can see it also has a slope of -2. Therefore, it is parallel to the original line.

### Example Question #785 : Geometry And Graphs

If a line has a slope of , what must be the slope of the perpendicular line?

Explanation:

The perpendicular line slope will be the negative reciprocal of the original slope.

Substitute the given slope into the equation.

### Example Question #786 : Geometry And Graphs

If the slope of a line is , what must be the slope of the perpendicular line?