2.1 Math Notes

2.1.1 Formula

• Sum of an arithmetic series\(S_n = \frac{n}{2}(a_1 + a_n)\), where \(S_n\) is the sum of the first \(n\) terms, \(n\) is the number of terms, \(a_1\) is the first term, and \(a_n\) is the last term.

2.1.2 Tips

• Recall and apply: Multiplying by a negative numbers changes the inequality sign. If \(mn<0, \frac{kn+ml}{mn}<mn \Rightarrow kn+ml > (mn)^2\)
• When the GRE writes a root sign, the question writers are indicating a non-negative root only
• If \(–3v > 0 \Rightarrow v < 0\)