This video introduces the three reciprocal trigonometric functions: the cotangent, the cosecant, and the secant. The video specifically defines each of these functions based on an angle in a right triangle.
Khan Academy exercise to practice:
1. Reciprocal Trigonometric Ratios: https://www.khanacademy.org/math/trigonometry/trigonometry-right-triangles/reciprocal-trig-ratios/e/reciprocal_trig_funcs
EulersAcademy.org