The ideas in this geometry lesson are taken from the Geometry ebook that I sell at MathMammoth.com.
This lesson plan does not contain all the problems the Geometry ebook
does.
Parallel and perpendicular lines
Free geometry lesson plan from HomeschoolMath.net
Two lines or line segments can either intersect (cross) each other or be parallel.
Think of the parallel lines as never meeting each other, no matter how
much you would continue them to both directions.
These lines intersect.
These lines are parallel.
What about these lines? Do they
intersect or are they parallel?
Try continuing the lines with your
ruler and see what happens.
These lines intersect and form four right
angles. They are perpendicular lines.
The little symbol
("corner") is used
to indicate a right angle.
We already know that two lines that
intersect form two pairs of vertical angles.
What happens if you have three lines, and two of them are parallel?
How many angles are there in the picture?
Measure the angles. Which ones have the same measure?
Again you see two parallel lines and one
line that intersects them both.
The two angles marked with a single arc are
corresponding
angles.
Also the two angles marked with the double
arc are corresponding angles.
All four angles have the same measure.
What kind of lines do you see in this picture?
How many angles?
Which angles have the same measure?
Mark the rest of the angles in this picture
and measure them.
The figure that is enclosed by the lines
is called a parallelogram.
A figure that has four sides so that the two
opposite sides are parallel and the other two
sides are parallel to each other, is called
a parallelogram.
What angles in the parallelogram have the
same measure?
If all the angles in a parallelogram are right
angles, it is called a rectangle.
If all the four angles are right angles and
all the four sides are the same, the figure is
called a square.
Example problem types
1. Calculate the other angles inside the parallelogram. Do not measure
since the pictures are not exact. What are the principles you can use?
a.
b.
2. a) Draw a parallelogram that has a 50 angle.
You can decide the length of the sides of the parallelogram. What else do
you need to know to be able to draw the parallelogram?
b) Draw a parallelogram that has a 118
angle.
5. Find one corresponding angle to each of the marked angles and mark
them the same way.
These pictures do have some extra lines there too but remember you need to look
for two parallel lines and a line that intersects them both.
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("corner") is used 
