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February 2012: triangle puzzle, Vi Hart & mathematical doodling, compound percent, geometry videos, and more

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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.

Measuring angles
Free geometry lesson plan from HomeschoolMath.net

Angles are measured in degrees. Remember how you can picture the one side of the angle as tracing out a circle or an arc of a circle. The FULL CIRCLE forms a 360 degree angle. Therefore a half circle or a straight angle is 180 degrees, and a fourth of a circle or a right angle is 90 degrees. Look at the pictures. We use the little circle to denote the degree after numbers.

This is a 1 degree angle!

This is a protractor. It is used to measure angles.
Note how it has the shape of half a circle;
therefore it only measures angles up to 180.
It has two sets of numbers: one set goes
from 0 to 180 one way, one set from 0 to 180
the other way. Which one you read depends on
where you place the one side of the angle you
are measuring.

[Picture available in the ebook]

To measure an angle, place the little circle or open hole of the protractor on the VERTEX of the angle. Place the zero line of the protractor on the ONE SIDE of the angle. Then read the measure where the other side hits the protractor scale. This angle is obviously an OBTUSE angle, so we read the scale at 127 degrees.

These pictures illustrate how to measure angles from triangles or other figures. The zero line of the protractor needs to be lined up with one side of the angle, and you read the set of numbers from your zero line on.

[Other pictures available in the ebook]


To draw an angle of 50, first draw a line segment that is to be the one side of the angle.	Then put the protractor so that its zero line matches with your line segment and that the vertex is in place. Then put a little mark at the 50 spot.	Take the protractor off and draw a line through your mark.

[Pictures available in the ebook]
These pictures illustrate drawing a 70 angle so that it shares a side with an existing angle.

Example problem types

1. Measure the following angles. If necessary, continue the sides of the angle..

2. Measure all the angles in these triangles.

3. Draw an angle of a) 35 b) 76 c) 137 d) 162

4. Here you see a pie with angles of 90, 75, 75, and 120 . Draw into the other pie diagram angles of 35 and 160 degrees. The picture already has a right angle. What will the fourth "pie piece angle" be?
[Pictures in the ebook]

Next geometry lesson

New! Times Tales is now on DVD!

The fast, FUN, and easy way to learn multiplication. Learn the upper times tales in two sittings using mnemonic stories.

Measuring angles Free geometry lesson plan from HomeschoolMath.net

Example problem types

Measuring angles
Free geometry lesson plan from HomeschoolMath.net