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# Algebraic Expressions

# Three-Sided Shapes

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.