Mathematical Induction http://www.cut-the-knot.org/induction.shtml
Explains the process of making and proving conjectures about the behavior of equations that a repetitive trait, such as summation formulas. Includes the rules for a valid induction and some examples.
Understanding Algebra by James Brennan http://www.jamesbrennan.org/algebra/
Covers the order of operations, working with plus and negative signs, solving for unknowns, straight line and polynomial functions, cartesian coordinates and simultaneous equations. Includes topical navigation, illustrations and charts.