Constructing  perpendiculars

Constructing perpendiculars to a line through a given point using only a straightedge and a compass is what I will show you here

There are two cases that you may encounter

Case #1: You are given a line and a point on the line

Constructing a perpendicular when point is on the line
Case #2: You are given a line and a point not on the line

Constructing a perpendicular when point is not on line
You will demonstrate both cases.

Let us start with case #1:

Step #1

Start with the following line and point P

Constructing a perpendicular when point is on the line
Open your compass to any radius or distance. Put the needle of the compass at point P and draw arcs on both sides of point P. Label the points where the arcs intersect the line C and D

Constructing a perpendicular when point is on line: step 1
Step #2

Open your compass to a radius or distance greater than the distance you chose to draw the arcs

After you have increased your compass opening, place the needle at C and draw and arc

Then, still using the same compass opening place the needle at D and draw another arc.

The two arcs should intersect as shown below. Call the point the two arcs intersect E

Constructing a perpendicular when point is on line: step 2
Step #3

Draw an line between P and E and you are done!

Constructing a perpendicular when point is on line: step 3
Case #2: You are given a line and a point not on the line

Start with the following line and point P not on the line

Constructing a perpendicular when point is not on the line
Step #1

Open your compass to a radius or distance greater than the distance from P to the line.

The distance you see below in red is the shortest distance from P to the line. That is what I mean by distance from P to the line; It is the shortest distance from P to the line which is usually done by drawing a straight line down

Constructing a perpendicular when point is not on the line: step 1
Open you compass to a distance greater than that

Step #2

After opening your compass to a distance greater than the shortest distance from P to the line, place the needle of the compass at P draw arcs that interset the line in two places

Constructing a perpendicular when point is not on the line: step 2
Call the points the arc intersect the line A and B

Step #3

Keeping the opening of the compass the same, place the needle at A and draw and arc

Then, place the needle at B and draw an arc. Call the point the two arc intersect E.

Constructing a perpendicular when point is not on the line: step 3
Step #4

Draw a line between point P and point E and you are done!

Constructing a perpendicular when point is not on the line: step 4
Here we go! Make sure you understand each step outlined above and follow them carefully. If you do this, you will have no problems whatsoever constructing perpendiculars.







Page copy protected against web site content infringement by Copyscape

Recent Articles

  1. Average age word problem

    Aug 09, 16 01:40 PM

    Average age of Dipu and Apu is 22 years. Average age of Dipu and Tipu is 24 years. Age of Dipu is 21 years. What are the ages of Apu, and tipu ? Let

    Read More



New math lessons

Your email is safe with us. We will only use it to inform you about new math lessons.