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11.3 Curves, Polygons and Symmetry Polygons Simple Definition A shape is simple if it doesn’t cross itself, except maybe at the endpoints. Closed Definition A shape is closed if the endpoints meet. Polygon Definition A polygon is a simple closed curve where all sides are line segments. There are no arcs allowed. Concave v. Convex Definition A polygon is convex if any segment connecting any two points in the interior of the curve lies entirely inside the curve. Definition A polygon is concave if any segment connecting two points of the interior of a curve passes outside of the curve Classification of Polygons by Sides Number of Sides 3 Polygon Name Classification of Polygons by Sides Number of Sides 3 Polygon Name triangle Classification of Polygons by Sides Number of Sides 3 4 Polygon Name triangle Classification of Polygons by Sides Number of Sides 3 4 5 Polygon Name triangle quadrilateral Classification of Polygons by Sides Number of Sides 3 4 5 6 Polygon Name triangle quadrilateral pentagon Classification of Polygons by Sides Number of Sides 3 4 5 6 7 Polygon Name triangle quadrilateral pentagon hexagon Classification of Polygons by Sides Number of Sides 3 4 5 6 7 8 Polygon Name triangle quadrilateral pentagon hexagon heptagon Classification of Polygons by Sides Number of Sides 3 4 5 6 7 8 9 Polygon Name triangle quadrilateral pentagon hexagon heptagon octagon Classification of Polygons by Sides Number of Sides 3 4 5 6 7 8 9 10 Polygon Name triangle quadrilateral pentagon hexagon heptagon octagon nonagon Classification of Polygons by Sides Number of Sides 3 4 5 6 7 8 9 10 11 Polygon Name triangle quadrilateral pentagon hexagon heptagon octagon nonagon decagon Classification of Polygons by Sides Number of Sides 3 4 5 6 7 8 9 10 11 12 Polygon Name triangle quadrilateral pentagon hexagon heptagon octagon nonagon decagon hendecagon Classification of Polygons by Sides Number of Sides 3 4 5 6 7 8 9 10 11 12 n Polygon Name triangle quadrilateral pentagon hexagon heptagon octagon nonagon decagon hendecagon dodecagon Classification of Polygons by Sides Number of Sides 3 4 5 6 7 8 9 10 11 12 n Polygon Name triangle quadrilateral pentagon hexagon heptagon octagon nonagon decagon hendecagon dodecagon n-gon Regular Polygons Definition A regular polygon is a polygon where all sides and interior angles are congruent. What is the name of a regular triangle? Regular Polygons Definition A regular polygon is a polygon where all sides and interior angles are congruent. What is the name of a regular triangle? • • • What is the name of a regular quadrilateral? Regular Polygons Definition A regular polygon is a polygon where all sides and interior angles are congruent. What is the name of a regular triangle? • • • What is the name of a regular quadrilateral? • • • • Exterior Angle Sum What is the exterior angle sum for a square? Exterior Angle Sum What is the exterior angle sum for a square? What is the exterior angle sum for a pentagon? Exterior Angle Sum What is the exterior angle sum for a square? What is the exterior angle sum for a pentagon? Conjecture? Exterior Angle Sum What is the exterior angle sum for a square? What is the exterior angle sum for a pentagon? Conjecture? Exterior Angle Sum The exterior angle sum for a convex polygon is 360◦ Triangle Classifications We can classify triangles in two ways - by the number of congruent sides and by the types of angles. What types of triangles are there? Triangle Classifications We can classify triangles in two ways - by the number of congruent sides and by the types of angles. What types of triangles are there? Types of Triangles scalene isosceles equilateral By Side no congruent sides at least two congruent sides all sides congruent acute right obtuse By Angle all angles acute one right angle one obtuse angle Triangle Classifications We can classify triangles in two ways - by the number of congruent sides and by the types of angles. What types of triangles are there? Types of Triangles scalene isosceles equilateral By Side no congruent sides at least two congruent sides all sides congruent acute right obtuse By Angle all angles acute one right angle one obtuse angle Important to note: your book correctly states that a triangle that is equilateral is also isosceles. Some books incorrectly say that these are disjoint descriptions. Quadrilateral Classifications That we want to do here is list all properties we know about the different quadrilaterals. Included in these properties we want to point out are: if opposite sides are parallel if opposite sides are congruent if opposite angles are congruent if adjacent angles are congruent if adjacent sides are perpendicular if diagonals bisect each other if diagonals are perpendicular if diagonals are congruent if there is at least one pair of parallel sides if there is at least one pair of congruent sides Parallelogram Parallelogram opposite sides congruent opposite angles are congruent diagonals bisect each other opposite sides are parallel Rectangle Rectangle opposite sides congruent opposite angles are congruent diagonals bisect each other opposite sides are parallel Rectangle opposite sides congruent opposite angles are congruent diagonals bisect each other opposite sides are parallel diagonals are congruent adjacent sides are perpendicular Rhombus Rhombus opposite sides congruent opposite angles are congruent diagonals bisect each other opposite sides are parallel Rhombus opposite sides congruent opposite angles are congruent diagonals bisect each other opposite sides are parallel adjacent sides congruent Square Square opposite sides congruent opposite angles are congruent diagonals bisect each other opposite sides are parallel diagonals are congruent adjacent sides are perpendicular Square opposite sides congruent opposite angles are congruent diagonals bisect each other opposite sides are parallel diagonals are congruent adjacent sides are perpendicular adjacent sides congruent Kite Kite two pairs of congruent adjacent sides diagonals are perpendicular one pair of congruent angles Trapezoid Trapezoid at least one pair of parallel sides Isosceles Trapezoid Isosceles Trapezoid at least one pair of parallel sides Isosceles Trapezoid at least one pair of parallel sides at least one pair of congruent sides base angles congruent Hierarchy for Triangles For triangles, here is the relationship between them based on sides. Triangle Scalene Triangle Isosceles Triangle Equilateral Triangle Hierarchy for Quadrilaterals Can you come up with a similar diagram for quadrilaterals? Hierarchy for Quadrilaterals Can you come up with a similar diagram for quadrilaterals? Quadrilateral Kite Trapezoid Parallelogram Rhombus Isosceles Trapezoid Rectangle Square Symmetries 1 Line symmetry 2 Rotational symmetry 3 Point symmetry Line Symmetry Line Symmetry A figure has line symmetry if we can draw a line that divides the figure in half. We can think of this as the line over which we can fold the figure to make it fold onto itself. How Many Lines of Symmetry? How Many Lines of Symmetry? Rotational Symmetry Rotational (Turn) Symmetry A figure has rotational symmetry if we can rotate the figure some number of degrees less than 360◦ and get the same exact polygon back in the same orientation. We describe the property as α degrees of turn symmetry. Rotational Symmetry? Rotational Symmetry? Point Symmetry Point Symmetry Point symmetry is the term that we use when a figure has 180◦ turn symmetry. Which of our figures have point symmetry? Diagonals Diagonal A diagonal is a line segment that joins to nonadjacenet vertices. Diagonals Diagonal A diagonal is a line segment that joins to nonadjacenet vertices. The question is, how many diagonals does a convex polygon have? Diagonals Diagonal A diagonal is a line segment that joins to nonadjacenet vertices. The question is, how many diagonals does a convex polygon have? Number of Diagonals A convex polygon with n sides we have n(n−3) 2 diagonals.