options: Understand radian measure of an angle as the length of the arc on the unit circle subtended by the angle.

Explain how the unit circle in the coordinate plane enables the extension of trigonometric functions to all real numbers, interpreted as radian measures of angles traversed counterclockwise around the unit circle.

Use special triangles to determine geometrically the values of sine, cosine, tangent for π/3, π/4 and π/6, and use the unit circle to express the values of sine, cosines, and tangent for π–x, π+x, and 2π–x in terms of their values for x, where x is any real number.

Use the unit circle to explain symmetry (odd and even) and periodicity of trigonometric functions.
problem_activity: Warm-up
The purpose of this warm-up is to prepare students for “unwrapping” the unit circle in the next activity and seeing what the graphs of
\(y=\cos(x)\)
and
\(y=\sin(x)\)
look like for the first time in this unit. Part of thinking of cosine and sine as functions is understanding their input and output. The prompts in this activity ask students to informally describe the output of the two trigonometric functions by focusing on each coordinate of a point on the unit circle.
Launch
Display the image for all to see.
Student Facing
Suppose there is a point
\(P\)
on the unit circle at
\((1,0)\)
.
[IMG]
Describe how the
\(x\)
-coordinate of
\(P\)
changes as it rotates once counterclockwise around the circle.
Describe how the
\(y\)
-coordinate of
\(P\)
changes as it rotates once counterclockwise around the circle.
Student Response
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Activity Synthesis
Invite students to share their descriptions, highlighting responses that use actual values such as 1, 0, and -1.


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