# User:Temperal/The Problem Solver's Resource2

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The Problem Solver's Resource
 Introduction | Other Tips and Tricks | Methods of Proof | You are currently viewing page 2.

## Simple Number Theory

This is a collection of essential AIME-level number theory theorems and other tidbits.

### Trivial Inequality

For any real $x$, $x^2\ge 0$, with equality iff $x=0$$. ===Arithmetic Mean/Geometric Mean Inequality=== For any set of real numbers$S$,$\frac{S_1+S_2+S_3....+S_{k-1}+S_k}{k}\ge \sqrt[k]{S_1\cdot S_2 \cdot S_3....\cdot S_{k-1}\cdot S_k}$with equality iff$S_1=S_2=S_3...=S_{k-1}=S_k$. ===Cauchy-Schwarz inequality=== For any real numbers$ (Error compiling LaTeX. ! Missing $inserted.)a_1,a_2,...,a_n$and$b_1,b_2,...,b_n$, the following holds:$\displaystyle(\sum a_i^2)(\sum b_i^2) \ge (\sum a_ib_i)^2$====Cauchy-Schwarz variation====

For any real numbers$(Error compiling LaTeX. ! Missing$ inserted.)a_1,a_2,...,a_n$and positive real numbers$b_1,b_2,...,b_n$, the following holds:$\displaystyle\sum\left({{a_i^2}\over{b_i}}\right) \ge {{\sum a_i^2}\over{\sum b_i}}\$.