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.
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: