Polygons, Perimeter, & Area

Polygon A closed plane figure formed by 3 or more segments

These are not polygons. Why not?

We most often name polygons by listing their vertices.  We most often name polygons by listing their vertices.  List the points in order  It doesn’t matter where you start or which way you go around.  We don’t normally use a symbol to name polygons.

Name this polygon.

Name this polygon. EMONSD DEMONS NOMEDS MEDSNO etc.

Identify the sides and angles of this polygon.

Identify the sides and angles of this polygon.

We normally classify polygons by the number of sides We normally classify polygons by the number of sides. In most cases Greek roots are used.

What kind of polygons are these?

What kind of polygons are these? Pentagon, octagon, and octagon

You can also represent the number of sides in a polygon by just saying n-gon where “n” is the number of sides. This is a 14-gon.

Polygons can be called convex or concave.

The perimeter of a polygon is the sum of the lengths of its sides.  The perimeter of a polygon is the sum of the lengths of its sides.  Distance around outside

Your book makes a big deal of specific formulas for squares, rectangles, and triangles SQUARE: P = 4s RECTANGLE: P = 2l + 2w TRIANGLE: P = a + b + c

Remember, though, you can just add up all the sides to find the perimeter of ANY polygon. (Use your common sense to find missing sides.)

Find the approximate perimeter

The word circumference is used to describe the distance around a circle.  Circumference and perimeter are essentially the same thing, but you use circumference with round shapes.

Formulas for circumference: C =  d C = 2  r

Find the exact circumference of these circles.

Find the exact circumference of these circles. 18 m 7 in

Find the approximate circumference of this circle.

Find the approximate circumference of this circle. 9 9  3. 14 28 Find the approximate circumference of this circle. 9 9  3.14 28.26 in

Area . the amount. of space. inside. a shape  Area  the amount of space inside a shape  Area is measured in square units (sq. ft., cm2, etc.)

There are 3 basic area formulas you MUST know: RECTANGLE: There are 3 basic area formulas you MUST know: RECTANGLE: A = l w TRIANGLE: A = ½ bh CIRCLE: A =  r2

Find these areas:

Find these areas: 12cm2 192cm2

Find this area: 36 sq. ft.

Find these areas:

Find these areas: 12cm2 84 sq. in.

Yes (same base and height)

Find these areas:

Find these areas: 36  113.04 cm2 81  254.34 sq. in.

You can find the area of more complicated shapes by dividing the shape up into rectangles, triangles, and circles, and adding up the areas of the parts.

Find this area:

Rectangle + Triangle Base of Triangle is 8 – 1 – 2 = 5

Find this area:

Circle + Triangle Radius of Circle is 7

REMEMBER: . Polygon (classifying, sides &. angles, concave, convex)  REMEMBER:  Polygon (classifying, sides & angles, concave, convex)  Perimeter/circumference  Area