1. Introduction
Mensuration is the branch of mathematics which deals with the study of Geometric shapes, their area, volume and related parameters.
Mensuration is the mathematical name for calculating the areas, volumes, length of sides, and other geometric parts of standard geometric shapes such as circles, spheres, polygons, prisms, cylinders, cones, etc., through the use of mathematical equations or formulas.

2. PLANE FIGURES

3. POLYGON
A polygon is a closed plane figure formed by line segments

4. Parts of a Polygon
Side (edge) – one of the line segments that make up the polygon
Adjacent sides – has a common endpoint
Vertices-endpoints of each side
Adjacent vertices – endpoints of a side
Diagonal-line segment joinin 2 non- adjacent vertices
Interior Angle – formed by 2 adjacent sides
Exterior Angle- adjacent to and supplementary to an interior angle

5. Types of Polygons Equiangular polygons- all angles are congruent
Equilateral polygons – all sides are equal
Regular polygon-both equiangular and equilateral
Irregular polygon- neither equiangular nor equilateral
Convex polygon- all interior angles are less than 180
Concave polygon- has atleast 1 interior angle that measures more than 180

6. Exercise

7. Naming Polygons Number of Sides Name of polygon n n-gon 3
Triangle or trigon 4
Quadrilateral or tetragon 5
pentagon 6
hexagon 7
heptagon 8
Octagon 9
Nonagon 10
Decagon

8. Naming Polygons

12. Similar Polygons

14. Properties of a Regular Polygon
- central angle
a- Apothem

15. Properties of a Regular Polygon
Perimeter:
Interior Angle
Sum of Interior Angles

16. Properties of a Regular Polygon
Area
Number of Diagonals