My tutoring students are often rattled by this chapter, but the confusion usually melts away once they see how arithmetic and geometric sequences are "the same but different". It's just two different sets of equations, but if you've got them at your fingertips (click on thumbnail to the right to see a pdf of all the formulas for sequences).
Also in this chapter there's a whole video *just* about SAT sequence questions since they're so common. Most students won't still remember their sequence formulas when the SAT comes around, but that's actually okay because SAT questions are usually designed so that the formulas wouldn't help you anyway.
In this video I cover how use all the formulas for arithmetic sequences and series. We'll learn what an nth term is, how to find it, how to find the sum of an arithmetic sequence, how to find the "common difference" d, and how to find arithmetic means.
Geometric Sequences & Series
In this video I cover how use all the formulas for geometric sequences and series. If you've already seen arithmetic sequences, this is going to be similar, except you'll definitely need a calculator, and the common difference gets replaced by the common ratio.
Sigma is just a Greek letter (I assume it's Greek since it's on the front of every frat house in the world) that looks like a cross between Z and E, and when you see it in math class it translates roughly to "you're screwed". Kidding! It actually means "sum", as in, "add all this stuff up." It's not too bad once you see how it works, but most teachers seem unable to make it non-confusing.
SAT-type Sequence Questions
I realize most students won't still remember their sequence formulas when the SAT comes around, but that's actually good, because SAT questions are usually designed so that the formulas wouldn't help you anyway!
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...)