Presentation on theme: "POLYGONS. A polygon is a closed plane figure made up of several line segments that are joined together. The sides do not cross one another. Exactly two."— Presentation transcript:
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2 A polygon is a closed plane figure made up of several line segments that are joined together. The sides do not cross one another. Exactly two sides meet at every vertex. Vertex : is the point at which two sides of a polygon meet.
3 Regular or Irregular If all angles are equal and all sides are equal, then it is regular, otherwise it is irregular TYPES OF POLYGONS
5 The sum of the angles of a triangle is 180 degrees. TRIANGLES Equilateral Triangle An equilateral triangle has three sides of equal length. This means that each angle is 60 degrees
6 Isosceles Triangle A triangle that has two sides of equal length. Therefore, it has two equal angles.
7 Scalene Triangle A scalene triangle has three sides with different lengths. Therefore, it has three different angles.
8 Acute Triangle : An acute triangle has three acute angles.
9 Obtuse Triangle: An obtuse triangle has an obtuse angle, in which one of the angles is more than 90 degrees.
10 Right Triangle : A right triangle has a right angle, in which one of the angles is 90 degrees.
11 A quadrilateral is a four-sided polygon in which the sum of all the angles is 360 º
14 http://www.youtube.com/watch?v=69lfTURDleshttp://www.youtube.com/watch?v=69lfTURDles (the song of polygons)
15 The intersection of the altitudes is the orthocenter. orthocenter The intersection of the medians is the centroid.centroid The intersection of the angle bisectors is the center of the incenter. The circumcenter is the center of a circle passing through the three vertices of the triangle.circumcenter POINT, LINES AND CIRCLES ASSOCIATED WITH A TRIANGLE
16 Using Thales we can divide a segment in equal parts. STEPS: 1.Draw the given segment AB. This is the segment that we want to divide. 2.From point A draw an oblique ray (r). 3.Chose a measure with your compass and from point A draw arcs on the oblique ray as many arcs as parts you need. 4.Join the last point of the oblique ray with point B. 5.Draw parallels using your set square to the segment B7 from the other points on the ray. We use Thales Theorem to divide a given line segment into a number of equal parts Remember : THALES THEOREM
17 HOW TO CONSTRUCT A “n” SIDED REGULAR POLYGON http://www.educacionplastica.net/zirkel/divCir_sol.html 1- Draw a circumference and its diameter AB. Divide the diameter in as many parts as sides has the polygon (Thales Theorem). 2- With center at points A and B and radius the diameter´s length, draw both arcs which intersect at point C. 3- Join point C with the second division on the diameter, and extend it so that it cuts the circumference at point E. 4. The segment AE is the side of the required polygon. Check the following link to see more ways to construct regular polygons: http://www.educacionplastica.net/poligonos.htm#pri
18 STAR POLYGONS - A star -shaped polygon is formed by joining together the non-consecutive vertices in a regular polygon. - To construct a star polygon inscribed in a circumference, we need to follow the same steps to draw a regular polygon, it depends on how many points of a star we want to draw. - So we must start finding the star points as they were the polygon vertices. A D B C
19 - Follow the same steps you follow to draw a pentagon. - You have now points A, B, C, D and E. - Join the non-consecutive vertices as follows: A-D, E-C D-B, C-A and B-E FIVE STAR POLYGON CD E
20 SIX POINTS STAR POLYGON - Follow the same steps you follow to draw an hexagon. - You have now points A,F,C B,D and E. - Join the non-consecutive vertices as follows: A-C, C-D,D-A,E-F,F-B and B-E A F C B D E
21 EIGHT POINTS STAR POLYGON - After the first steps common to all regular polygons we get four rect angles and points A,B,C,D. - Find the angle bisector of each angle.Those rects intersect the circumference at points E, F,G and H. - Join together the non- consecutive vertices to find an eight points star polygon: A-B, B-C, C-D, D-A and E-F, F-G, G-H, H-E
22 LONG EIGHT POINTS STAR POLYGON - Follow the same steps you follow to draw an eight points star polygon. - We´ll name these points with numbers this time, to make easier the joining.
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- Join the 1+3 non-consecutive points beginning at number 1. A E F B G C H D E