Section 1.6 Two-Dimensional Figures

 Derived from a Greek word meaning “many sides”.  Polygon- closed figure formed by a finite number of coplanar segments called sides such that:  The sides that have a common endpoint are noncollinear  Each side intersects exactly two other sides  Vertex of the polygon- vertex of each angle

 Polygons are classified by the number of sides.  3-Triangle,9-Nonagon  4-Quadrilateral, 10-Decagon  5-Pentagon,11- Hendecagon  6-Hexagon, 12-Dodecagon  7-Heptagon  8-Octagon

 Polygons are named by the letters of its consecutive (in order) vertices.

 Concave- some lines (when extended) pass through the interior of the polygon  Convex- no points of the lines (when extended) are in the interior.

 Equilateral polygon - all sides are congruent.  Equiangular polygon - all angles are congruent.  Regular polygon - convex, equilateral, and equiangular.  Irregular – everything else

 Name each polygon by its number of sides, then state whether it is convex or concave, regular or irregular.

 Perimeter - sum of the lengths of all the sides  Units stay the same.  Circumference -distance around a circle  Units stay the same.  Area - number of square units needed to cover a surface  Units are squared.

TriangleSquareRectangleCircle Perimeter P = b + c +dP = 4sP=2l +2wC= π d Area A= 1/2bhA=s 2 A=lwA= π r 2

 Find the area and perimeter (or circumference) of each figure. 12.4ft 18.9ft 5cm 12cm 6m

 What is the perimeter of a rectangle if its length is half its width and its area is 48 in 2 ?

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