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.

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.

[Pictures available in the ebook]

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