This is the second book in the series of Althea's Math Mysteries.  Althea and her friends - Kiara, Sofia, and Aiden - get together to explore geometry, pi, and trigonometry, with Mom's help.

Links mentioned in the book, in order by chapter.

If you'd like to form a math circle like the group of friends Althea worked with, do it! (I could maybe help you find someone who'd enjoy helping your circle, or maybe you can do it without an adult leading. Or maybe you're an adult. You could get a few friends together and play with these activities. We are never too old!)

Activities:

• Geometry Challenges site  

  • (Aiden finds this for the pentagon. But why does it work?!)

  • Here's another construction site with lots more challenges (sadly, they must be done in order)

• Drawing and tearing. Proof that angles in a triangle add to 180.

• Alternate Geometries (find good sites)

  • Proof that square root of 2 is irrational (Here's a related article.)

  • History of Mathematicians Thinking About Euclid's 5th Postulate

• Measuring circles to define π

• Finding π’s value, with circles and triangles, and some proofs along the way

• Measuring angles. Making an inclinometer.

• Trigonometry

Extra Activities (not in the book):

• Making an angle of a given size,   and a harder (timed) activity

• Estimating the size of a given angle

History:

• Some Highlights

• Who Was Euclid?

• Euclid's Elements

Background:

• Why there's a bit more than 12 hours of daylight on the equinox.