- Topics At a Glance
- Variables
- Variables as Unknown Quantities
- Variable Notations
- Constants
- Expressions and Equations
- Rearranging Expressions
- Commutative Properties
- Associative Properties
- Distributive Properties
- Factoring (Distributive Property in Reverse)
- Combining Like Terms
- Eliminating Parentheses
- Simplifying
- Equations, Functions, and Formulas
- Equations
- Functions
- Independent and Dependent Variables
- Formulas
- Applications to Toolbox
- Evaluating Expressions by Substitution
- Evaluating Formulas by Substitution
**Geometric Formulas**- Four-Sided Shapes
**Three-Sided Shapes**- Circles
- Unit Conversion
- Temperatures
- Weights
- Distances and Speeds
- Money
- In the Real World
- I Like Abstract Stuff; Why Should I Care?
- How to Solve a Math Problem

We call a three-sided shape a **triangle** You know these guys; they have been made famous thanks to pizza.

The perimeter of a triangle is the sum of its three sides. The area *A* of a triangle is given by the formula

*.*

This formula is the way it is because the triangle fills exactly half of a rectangle with side lengths *b* and *h*, as shown below.