GEOMETRYSection 1.6
Two-Dimensional Figures
POLYGONS 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
EXAMPLE 1 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 sidesUnits stay the same.
Circumference -distance around a circleUnits stay the same.
Area - number of square units needed to cover a surfaceUnits are squared.
FORMULASTriangle Square Rectangl
eCircle
Perimeter P = b + c
+dP = 4s P=2l
+2wC= πd
Area A= 1/2bh A=s2 A=lw A=πr2
THE PYTHAGOREAN THEOREM For any right triangle,
EXAMPLE 3 Find the area and perimeter (or
circumference) of each figure.
12.4ft
18.9ft
5cm
12cm
6m
EXAMPLE 4 What is the perimeter of a
rectangle if its length is half its width and its area is 48 in2?
HOMEWORK Page 61: 1-10 all, 12- 26 evens,
32-42 evens
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