Challenge the class to figure out sin57 with just a ruler and protractor - no calculator. Hopefully some bright spark will put the equipment together with last night's homework, and draw a right-angled triangle with a diagonal of 1.

So, same challenge - cos23. This time, draw the triangle yourself, putting the 'angle' in the same place.

Finally, draw the unit circle in. Pick a third point on the circle, in the same quadrant. Draw an 'x' there.

"What's special about this point?"

Hopefully someone (perhaps someone who's done the homework) will now tell you that you should draw the triangle, and that the two straight sides will give you sin and cos of the angle.

## Alert!

**Hello, reader! If you intend to post a link to this blog on Twitter, be aware that for utterly mysterious reasons, Twitter thinks this blog is spam, and will prevent you from linking to it. Here's a workaround: change the .com in the address to .ca. I call it the "Maple Leaf Loophole." And thanks for sharing!**## Wednesday, February 2, 2011

### We Have a Winner

Alex, on Files for Riley's Intro to Trig, asking the question backwards and displaying the kind of lesson-design genius that I wish came easily to me:

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