There is notation that corresponds to these ideas, for example,

reads "

*m*perpendicular". To find the slope of the perpendicular line simply reciprocate the number and change the sign.

[

**Interactive**: Perpendicular Lines ]**Find the corresponding perpendicular slope**.

Of course, just use the same slope if you are asked to find the slope a parallel line.

**Are the lines parallel, perpendicular or neither?**

**Find the slope of the line perpendicular.**

Now we use these facts and the formula for equations of lines to find equations given certain geometric information. Recall,

**Example**: Find the equation of the line perpendicular to

*y*= −1/4

*x*+ 2 passing through the point (−1,−5).

This three step process using slope-intercept form always works. We could find this equation using point-slope form as well as demonstrated below.

**Example**: Find the equation of the line perpendicular to

*y*= −1/4

*x*+ 2 passing through the point (−1, −5).

Notice that the answer

*y*= 4

*x*− 1 is the same using either method.

**Instructional Video**: Parallel and Perpendicular Lines - Part 2

**Find the equation of the line**. (Using slope-intercept form.)

**Find the equation of the line**. (Using point-slope form.)

**Video Examples on YouTube**: