Practice this lesson yourself on KhanAcademy.org right now: https://www.khanacademy.org/math/trigonometry/less-basic-trigonometry/trig-symmetry-periodicity/e/symmetry-and-periodicity-of-trig-functions?utm_source=YT&utm_medium=Desc&utm_campaign=Trigonometry Watch the next lesson: https://www.khanacademy.org/math/trigonometry/less-basic-trigonometry/trig-symmetry-periodicity/v/tan-symmetries-unit-circle?utm_source=YT&utm_medium=Desc&utm_campaign=Trigonometry Missed the previous lesson? https://www.khanacademy.org/math/trigonometry/trig-function-graphs/long_live_tau/v/pi-is-still-wrong?utm_source=YT&utm_medium=Desc&utm_campaign=Trigonometry Trigonometry on Khan Academy: Big, fancy word, right? Don’t be fooled. Looking at the prefix, tri-, you could probably assume that trigonometry (“trig” as it’s sometimes called) has something to do with triangles. You would be…