Wyzant
Wyzant: Basics of Equations
This tutorial from WyzAnt contains a walk-through of the basics of solving algebraic equations. Examples are given and the tutorial ends with an interactive worksheet that contains an answer key.
Wyzant
Wyzant: Basics of an Algebra Equation
This site provides a diagram of a basic equation, followed by a full explanation.
Math2
Math2: Circles
This site has many useful formulas and examples relating to circles, including related definitions, circumference of a circle, area of a circle, length of a circular arc, area of a circular sector, equation of a circle in cartesian...