Geometry Notes Section 1 6 What youll learn

Geometry Notes Section 1 -6

What you’ll learn. . . How to identify and name polygons n Find perimeters of polygons n

Vocabulary Polygon n Concave n Convex n n-gon n Regular polygon n perimeter n

Polygons n Examples n Non examples:

DEFN: POLYGON n To name a ¨ a closed figure in a plane polygon, list ¨ formed by connecting line segments endpoint consecutive Consecutive to endpoint (these line segments only sides vertices intersect the other line segments at the A polygon is endpoints) n E Parts of Polygons ¨ Each line. Psegment is a called a SIDE N ¨ Each endpt where sides meet is a VERTEX Diagonal Consecutive ¨ Diagonal Consecutive Vertices Angles ¨ Interior ¨ Exterior A T The name of this pentagon is PENTA.

Convex vs. Concave Polygons n Convex Polygons: n A polygon is convex if no diagonal is outside the polygon n Concave Polygons: n A polygon is concave if at least one diagonal is outside the polygon

Sides Names of Polygons Name 3 Triangle 8 Octagon 4 Quadrilateral 9 Nonagon 5 Pentagon 10 Decagon 6 Hexagon 12 Dodecagon 7 Heptagon n n-gon

DEFN: Regular Polygon n A polygon is regular if. . . It is convex Not Equilateral or n It is equilateral Not Equilateral Regular or Not? Not!! YES Regular or Not? Equiangular Equilateral – all sides are the same length n It¨is equiangular n ¨ Equiangular measure – all angles are the same

DEFN: Perimeter of a Polygon n Find perimeter The the perimeter of a of polygon PENTA. is the sum of all sides. N 6 in E Bet you’ve never heard that 6 in one before T 5 in P n 5 in 7 in A Perimeter = 5+6+6++5+7=29 inches

Perimeter revisited… n To find perimeter for a polygon in a coordinate plane ¨Remember, perimeter is the sum of the I told you, this lengths of all sides. . . formula would be ¨Find the length (or measure) of each used all year. . . side n You may have to use the distance formula

Example Find the perimeter of PQR if P(-5, 1), Q(-1, 4) say and Please 3, R(-6, -8). Please say Perimeter = sum of all sides How many sides does a triangle have? 3 So we have to find the length of 3 sides. Oh, yes. . . The distance formula— 3 times. Find PQ, QR, and PR using the distance formula.

Have you learned. . . How to identify and name polygons? n Find perimeters of polygons? n Assignment: Worksheet 1. 6 n