What formulas do I need to know for SAT subject math 2?
For a comprehensive list of formulas, I’d recommend the Kaplan book. Generally speaking, you should know basic algebra formulas (like rules of exponents, the quadratic formula), two and three dimension geometry formulas (area, perimeter, volume, surface area), coordinate geometry formulas (slope, distance, midpoint), trig identities, logarithms rules, formulas for arithmetic and geometric sequences, and be very comfortable with percents, averages, probability, and permutations/combinations. It’s a lot of material, but chances are you’ve seen most if not all of it in school. Good luck!
