Page 1 Points to Remember : 1. A closed figure. A figure which begins and ends at the same point is called a close figure. e.g. circle, triangle, quadrilaterals etc. are all closed figures. 2. Polygon. A simple closed figure formed of three or more line segments is called a polygon. (i) Sides. The line segments formed a polygon are called its sides. (ii) Vertices. The meeting point of a pair of the sides of a polygon is called its vertex. (iii) Adjacent sides. Any two sides of a polygon having a common end point or vertex are called its adjacent sides. (iv) Diagonals. A line segment joining two non-adjacent vertices of a polygon is called its diagonal. 3. Triangle. A polygon of 3 sides is called a triangle. 4. Quadrilateral. A polygon of 4 sides is called a quadrilateral. 5. Pentagon. A polygon of 5 sides is called a pentagon. 6. Hexagon. A polygon of 6 sides is called a hexagon. 7. Heptagon. A polygon of 7 sides is called a heptagon. 8. Octagon. A polygon of 8 sides is called an octagon. Note. A triangle has 3 sides, 3 angles and 3 vertices. A quadrilateral has 4 sides, 4 angles and 4 vertices. A pentagon has 5 sides, 5 angles and 5 vertices. A hexagon has 6 sides, 6 angles and 6 vertices. A heptagon has 7 sides, 7 angles and 7 vertices. An octagon has 8 sides, 8 angles and 8 vertices. EXERCISE 15 Q. 1. Which of the following are simple closed figures ? Sol. (a), (b), (d) and (f) are simple closed figures. Page 2 Points to Remember : 1. A closed figure. A figure which begins and ends at the same point is called a close figure. e.g. circle, triangle, quadrilaterals etc. are all closed figures. 2. Polygon. A simple closed figure formed of three or more line segments is called a polygon. (i) Sides. The line segments formed a polygon are called its sides. (ii) Vertices. The meeting point of a pair of the sides of a polygon is called its vertex. (iii) Adjacent sides. Any two sides of a polygon having a common end point or vertex are called its adjacent sides. (iv) Diagonals. A line segment joining two non-adjacent vertices of a polygon is called its diagonal. 3. Triangle. A polygon of 3 sides is called a triangle. 4. Quadrilateral. A polygon of 4 sides is called a quadrilateral. 5. Pentagon. A polygon of 5 sides is called a pentagon. 6. Hexagon. A polygon of 6 sides is called a hexagon. 7. Heptagon. A polygon of 7 sides is called a heptagon. 8. Octagon. A polygon of 8 sides is called an octagon. Note. A triangle has 3 sides, 3 angles and 3 vertices. A quadrilateral has 4 sides, 4 angles and 4 vertices. A pentagon has 5 sides, 5 angles and 5 vertices. A hexagon has 6 sides, 6 angles and 6 vertices. A heptagon has 7 sides, 7 angles and 7 vertices. An octagon has 8 sides, 8 angles and 8 vertices. EXERCISE 15 Q. 1. Which of the following are simple closed figures ? Sol. (a), (b), (d) and (f) are simple closed figures. Q. 2. Which of the following are polygons ? Sol. (a), (b) and (c) are polygons. Q. 3. Fill in the blanks : (i) A polygon is a simple closed figure formed by more than.............line segments. (ii) A polygon formed by three line segments is called a............. . (iii) A polygon formed by four line segments is called a............. . (iv) A triangle has.............sides and............. angles. (v) A quadrilateral has.............sides and .............angles. (vi) A figure which ends at the starting point is called a............. . Sol. (i) two (ii) triangle (iii) quadrilateral (iv) 3, 3 (v) 4, 4 (vi) closed figure.Read More

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