# What is Geometry

Geometry is a branch of mathematics that deals with the study of shapes, sizes, positions, angles, and properties of space. It explores the relationships and properties of geometric figures such as points, lines, angles, surfaces, and solids. Geometry is a fundamental part of mathematics and has practical applications in various fields such as architecture, engineering, computer graphics, physics, and many others.

Here’s a breakdown of some key concepts in geometry along with examples, questions, and answers:

1. **Points, Lines, and Planes:**

– **Point:** A point is a location in space that has no size or shape. It is represented by a dot and named using capital letters.

– **Line:** A line is a straight path that extends infinitely in both directions. It is represented by a straight line with two arrowheads.

– **Plane:** A plane is a flat surface that extends infinitely in all directions. It is represented by a shape that looks like a tabletop.

**Example Question:** Identify the points, lines, and planes in the following diagram:

– Points: A, B, C, D

– Lines: AB, CD

– Planes: Plane ABC, Plane ADC

2. **Angles:**

– **Angle:** An angle is formed by two rays with a common endpoint called the vertex.

– **Types of Angles:** Angles can be classified based on their measurement:

– Acute Angle: Measures between 0 and 90 degrees.

– Right Angle: Measures exactly 90 degrees.

– Obtuse Angle: Measures between 90 and 180 degrees.

– Straight Angle: Measures exactly 180 degrees.

– Reflex Angle: Measures between 180 and 360 degrees.

**Example Question:** Classify the following angles as acute, obtuse, or right:

– Angle ( A) is acute.

– Angle ( B) is obtuse.

– Angle ( C) is a right angle.

3. **Polygons:**

– **Polygon:** A polygon is a closed geometric figure made up of straight line segments.

– **Types of Polygons:** Polygons can be classified based on the number of sides they have:

– Triangle (3 sides)

– Pentagon (5 sides)

– Hexagon (6 sides)

– Heptagon (7 sides)

– Octagon (8 sides)

– Nonagon (9 sides)

– Decagon (10 sides)

**Example Question:** Identify the type of polygon shown below:

**Answer:** This is a hexagon because it has six sides.

4. **Circle:**

– **Circle:** A circle is a set of points in a plane that are equidistant from a fixed point called the center.

– **Radius:** The distance from the center of the circle to any point on the circle.

– **Diameter:** The distance across the circle passing through the center.

– **Circumference:** The perimeter of the circle.

– **Area:** The space enclosed by the circle.

**Example Question:** Calculate the circumference and area of a circle with a radius of 5 units (use ( pi = 3.14 )).

– Circumference: ( C = 2 pi r = 2 times 3.14 times 5 = 31.4 ) units

– Area: ( A = pi r^2 = 3.14 times 5^2 = 78.5 ) square units

5. **Solid Figures:**

– **Cube:** A solid figure with six square faces.

– **Rectangular Prism:** A solid figure with two parallel rectangular bases and four rectangular faces.

– **Cylinder:** A solid figure with two circular bases and a curved surface.

– **Sphere:** A solid figure where all points are equidistant from the center.

**Example Question:** Calculate the volume of a cube with a side length of 3 units.