Learning goals: Teacher Facing Comprehend that cosine and sine are defined as the $x$- and $y$-coordinates of a point $P$ on the unit circle at $\theta$ radians. Understand the Pythagorean Identity as a connection between the Pythagorean Theorem and the coordinates of points on a unit circle. Use the Pythagorean Identity to determine if a point is on the unit circle. Full lesson plan (warm-up, activities, synthesis, cool-down prompt) from Alg2.6 Trigonometric Functions, Algebra 2.