Double-Angle, Half-Angle, and Sum/Difference Formulas
So many formulas, so little time! Luckily you'll never see most of these again - even in Calculus - so the key is to figure out exactly which ones your teacher expects you to have memorized, and go from there. In the videos below, I take you through the most important ones, and show you how they're used in typical homework and test questions.
Of all the formulas in the Trig Identities chapter, the double-angle formulas are the only ones you'll ever see again in Calculus. In this video we'll take a look at the double-angle formulas for sine and cosine and work a few examples. And I throw a proof in there, just in case you're in honors and have an aggro teacher.
Half-Angle Formulas for Sine, Cosine & Tangent
"Half-angle formula" and "double-angle formula" sound pretty similar, so you'd think they'd be equally important. Nope! But I give the half-angle formulas their own video anyway because they seem to generate the most confusion vis-a-vis which angle to pick for θ and θ/2.
Sum & Difference Formulas, and Even-Odd Properties
This video contains the remainder of the "popular" sum and difference formulas that almost every trig teacher seems to go over for sine, cosine & tangent. If you have to memorize these, I tell you tips for that as well, but most teachers will give them to you. Also, what do "even" and "odd" have to do with trig?
If you do not have an account, you should get one, because it is awesome! You can save a playlist for each test or each chapter, and save your "greatest hits" into a "watch right before the final" list (not that we recommend cramming, but when in Rome...)