See Sal solve a bunch of very challenging geometry and algebra problems that involve trigonometry.
4450_Trig_challenge_problem_system_of_equations.html
4447_Trig_challenge_problem_arithmetic_progression.html
4445_Trig_challenge_problem_area_of_a_hexagon.html
4449_Trig_challenge_problem_multiple_constraints.html
4446_Trig_challenge_problem_cosine_of_angle_sum.html
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