Sines and cosines pop on your calculator screen like magic. Here is a visual way to understand what these trigonometric ratios mean in a unit circle. A ruler slides back and forth in the horizontal slot. You can read the sine and cosine of the angle on the ruler.

- Cut out the pattern pieces.
- Cut out the horizontal slot out of the larger piece to form a slot that the ruler will slide in.
- Cut along the thick lines on the vertical ruler.
- Fold the tabs on the ruler. Dashed lines are valley folds and dot-dashed lines are mountain folds.
- Slip the tabs of the ruler into the slot on the larger piece.
- Line up the ruler so the left edge touches the circle at the angle you are interested in.
- Determine the sine of the angle by reading the value on the vertical ruler.
- Determine the cosine of the angle by reading the value on the horizontal ruler.

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