Circles In Maths
Circles in Maths
A circle is a plane figure that is defined by the distance from a fixed point (the center) to any point on the figure. The distance from the center to any point on the circle is called the radius.
Circles are important in mathematics because they are used to represent many different things, such as the shape of a coin, the path of a planet around the sun, or the crosssection of a cylinder.
The circumference of a circle is the distance around the circle, and it is calculated by multiplying the diameter (the distance across the circle through the center) by pi (a mathematical constant approximately equal to 3.14).
The area of a circle is the amount of space inside the circle, and it is calculated by multiplying pi by the square of the radius.
Circles are also used in many different formulas and equations, such as the Pythagorean theorem and the equation for the volume of a sphere.
Circle Definition
Circle Definition
A circle is a plane figure that is defined by the distance from a fixed point (the center) to any point on the figure. The distance from the center to any point on the circle is called the radius.
Circles can be drawn using a compass, which is a tool that has two arms that can be adjusted to different lengths. One arm of the compass is fixed at the center of the circle, and the other arm is used to draw the circle.
Circles can also be defined mathematically. The equation of a circle is:
(x  h)^2 + (y  k)^2 = r^2
where:
 (h, k) is the center of the circle
 r is the radius of the circle
Examples of Circles
Circles are found all around us. Here are a few examples:
 The sun is a circle.
 The moon is a circle.
 A coin is a circle.
 A basketball is a circle.
 A bicycle wheel is a circle.
Properties of Circles
Circles have a number of properties, including:
 The circumference of a circle is equal to 2πr, where r is the radius of the circle.
 The area of a circle is equal to πr^2, where r is the radius of the circle.
 The diameter of a circle is equal to twice the radius.
 The tangent to a circle at a point is perpendicular to the radius at that point.
Applications of Circles
Circles are used in a variety of applications, including:
 Measuring the distance to the moon
 Determining the time of day
 Designing gears
 Building bridges
 Creating art
Circles are a fundamental part of geometry and have a wide range of applications in the real world.
How to Draw a Circle?
How to Draw a Circle
A circle is a twodimensional shape with a fixed distance from a central point to any point on the circle. Circles are often used to represent objects that are round, such as balls, coins, and planets.
There are a few different ways to draw a circle. One way is to use a compass. A compass is a tool that has two arms that can be adjusted to different lengths. To draw a circle with a compass, follow these steps:
 Place the compass point on the paper where you want the center of the circle to be.
 Adjust the arms of the compass to the desired radius of the circle.
 Hold the compass steady and rotate it around the center point.
 The compass will draw a circle on the paper.
Another way to draw a circle is to use a string. To draw a circle with a string, follow these steps:
 Cut a piece of string that is twice the length of the desired radius of the circle.
 Tie the ends of the string together to form a loop.
 Place the loop of string around a pencil or pen.
 Hold the pencil or pen at the center of the circle and pull the string taut.
 Rotate the pencil or pen around the center point, keeping the string taut.
 The string will draw a circle on the paper.
If you don’t have a compass or a string, you can also draw a circle by hand. To draw a circle by hand, follow these steps:
 Draw a square.
 Connect the opposite corners of the square with two lines.
 The point where the two lines intersect is the center of the circle.
 Draw a circle around the center point, using the length of one side of the square as the radius.
Here are some examples of circles:
 A ball
 A coin
 A planet
 A wheel
 A clock face
 A target
 A donut
 A pizza
Circles are used in many different areas of mathematics, science, and engineering. They are also used in art, design, and architecture.
Parts of Circle
Parts of a Circle
A circle is a plane figure that is defined by the distance from a fixed point (the center) to any point on the circle. The radius of a circle is the length of the line segment from the center to any point on the circle. The diameter of a circle is the length of the line segment that passes through the center and has endpoints on the circle.
Parts of a Circle:

Center: The center of a circle is the fixed point from which all points on the circle are equidistant. It is often denoted by the letter “O”.

Radius: The radius of a circle is the distance from the center to any point on the circle. It is often denoted by the letter “r”.

Diameter: The diameter of a circle is the length of the line segment that passes through the center and has endpoints on the circle. It is often denoted by the letter “d”. The diameter of a circle is twice the length of the radius.

Chord: A chord of a circle is a line segment that has both endpoints on the circle.

Secant: A secant is a line that intersects a circle at two points.

Tangent: A tangent is a line that intersects a circle at one point and is perpendicular to the radius at that point.

Arc: An arc is a portion of a circle. It is measured in degrees.

Sector: A sector is a region of a circle that is bounded by two radii and an arc.

Segment: A segment is a region of a circle that is bounded by a chord and an arc.
Examples:

The center of a circle can be found by intersecting two perpendicular diameters.

The radius of a circle can be found by measuring the distance from the center to any point on the circle.

The diameter of a circle can be found by measuring the length of the line segment that passes through the center and has endpoints on the circle.

A chord of a circle can be found by drawing a line segment that has both endpoints on the circle.

A secant can be found by drawing a line that intersects a circle at two points.

A tangent can be found by drawing a line that intersects a circle at one point and is perpendicular to the radius at that point.

An arc can be found by measuring the angle between two radii.

A sector can be found by measuring the angle between two radii and the length of the arc that is bounded by the radii.

A segment can be found by measuring the angle between two radii and the length of the chord that is bounded by the radii.
Circle Formulas
Circle Formulas
A circle is a plane figure that is defined by the distance from a fixed point (the center) to any point on the figure. The radius of a circle is the distance from the center to any point on the circle. The diameter of a circle is the distance across the circle through the center.
Circumference of a Circle
The circumference of a circle is the distance around the circle. The circumference of a circle is given by the formula:
C = 2πr
where:
 C is the circumference of the circle
 r is the radius of the circle
 π is a mathematical constant approximately equal to 3.14159
Example:
Find the circumference of a circle with a radius of 5 cm.
C = 2πr
C = 2π(5 cm)
C = 10π cm
C ≈ 31.42 cm
Area of a Circle
The area of a circle is the amount of space inside the circle. The area of a circle is given by the formula:
A = πr²
where:
 A is the area of the circle
 r is the radius of the circle
 π is a mathematical constant approximately equal to 3.14159
Example:
Find the area of a circle with a radius of 5 cm.
A = πr²
A = π(5 cm)²
A = 25π cm²
A ≈ 78.54 cm²
Sector of a Circle
A sector of a circle is a region of the circle that is bounded by two radii and an arc. The area of a sector of a circle is given by the formula:
A = (θ/360)πr²
where:
 A is the area of the sector
 θ is the measure of the central angle of the sector in degrees
 r is the radius of the circle
 π is a mathematical constant approximately equal to 3.14159
Example:
Find the area of a sector of a circle with a radius of 5 cm and a central angle of 60 degrees.
A = (θ/360)πr²
A = (60/360)π(5 cm)²
A = (1/6)π(25 cm²)
A ≈ 13.09 cm²
Segment of a Circle
A segment of a circle is a region of the circle that is bounded by two radii and an arc. The area of a segment of a circle is given by the formula:
A = (θ/360)πr²  (1/2)r²sinθ
where:
 A is the area of the segment
 θ is the measure of the central angle of the segment in degrees
 r is the radius of the circle
 π is a mathematical constant approximately equal to 3.14159
Example:
Find the area of a segment of a circle with a radius of 5 cm and a central angle of 60 degrees.
A = (θ/360)πr²  (1/2)r²sinθ
A = (60/360)π(5 cm)²  (1/2)(5 cm)²sin60°
A = (1/6)π(25 cm²)  (1/2)(25 cm²)(√3/2)
A ≈ 13.09 cm²  6.55 cm²
A ≈ 6.54 cm²
Solved Examples
Solved Examples
Solved examples are a powerful tool for learning. They provide a concrete illustration of how a concept or principle works, and they can help students to identify and correct their mistakes. In addition, solved examples can help students to develop their problemsolving skills and to gain confidence in their ability to apply their knowledge to new situations.
Here are some examples of solved examples:
 Math: A math teacher might provide a solved example of how to solve a quadratic equation. The example would show the student how to factor the equation, find the roots, and write the solution in the correct format.
 Science: A science teacher might provide a solved example of how to design and conduct an experiment. The example would show the student how to identify the variables, control for confounding factors, and collect and analyze data.
 History: A history teacher might provide a solved example of how to write a historical essay. The example would show the student how to choose a topic, research the topic, and organize and present their findings in a clear and concise manner.
 Language Arts: A language arts teacher might provide a solved example of how to write a short story. The example would show the student how to create a plot, develop characters, and use figurative language to create a vivid and engaging story.
Solved examples can be a valuable resource for students of all ages and abilities. They can help students to learn new concepts, develop their problemsolving skills, and gain confidence in their ability to apply their knowledge to new situations.
Here are some tips for using solved examples effectively:
 Read the example carefully. Make sure that you understand each step of the solution.
 Identify the key concepts and principles. What is the example trying to teach you?
 Compare the example to your own work. Are you making the same mistakes? If so, how can you correct them?
 Practice applying the concepts and principles to new situations. The more you practice, the better you will become at solving problems on your own.
Solved examples are a powerful tool for learning. By using them effectively, you can improve your understanding of new concepts, develop your problemsolving skills, and gain confidence in your ability to apply your knowledge to new situations.
Frequently Asked Questions on Circles
What is called a circle?
A circle is a plane figure that is defined by the distance from a fixed point (the center) to any point on the figure. The distance from the center to any point on the circle is called the radius.
Circles are often used to represent objects that are round, such as balls, coins, and planets. They are also used in mathematics to represent sets of points that are equidistant from a given point.
Here are some examples of circles:
 A basketball is a circle.
 A coin is a circle.
 The Earth is a circle.
 The sun is a circle.
 A clock face is a circle.
 A target is a circle.
Circles have a number of properties that make them unique. For example, all circles are symmetrical around their center. This means that if you draw a line through the center of a circle, the two halves of the circle will be mirror images of each other.
Circles also have a constant radius. This means that the distance from the center of a circle to any point on the circle is always the same.
Circles are important in many areas of mathematics and science. They are used in geometry to study the properties of shapes, in trigonometry to study the relationships between angles and sides of triangles, and in calculus to study the derivatives and integrals of functions.
Circles are also used in many applications in the real world. For example, they are used in engineering to design gears and other mechanical parts, in architecture to design buildings and bridges, and in navigation to determine the location of ships and airplanes.
What are the different parts of a circle?
Parts of a Circle
A circle is a plane figure that is defined by the distance from a fixed point (the center) to any point on the figure. The distance from the center to any point on the circle is called the radius.
The following are the different parts of a circle:
 Center: The center of a circle is the fixed point from which all other points on the circle are equidistant.
 Radius: The radius of a circle is the distance from the center to any point on the circle.
 Diameter: The diameter of a circle is the distance across the circle through the center. The diameter is twice the length of the radius.
 Chord: A chord is a line segment that connects two points on a circle.
 Secant: A secant is a line that intersects a circle at two points.
 Tangent: A tangent is a line that intersects a circle at one point and is perpendicular to the radius at that point.
 Arc: An arc is a portion of a circle that is bounded by two points on the circle.
 Sector: A sector is a region of a circle that is bounded by two radii and an arc.
 Segment: A segment is a region of a circle that is bounded by a chord and an arc.
Examples
 The center of a circle can be represented by a point, such as O.
 The radius of a circle can be represented by a line segment, such as OA.
 The diameter of a circle can be represented by a line segment, such as AB.
 A chord can be represented by a line segment, such as CD.
 A secant can be represented by a line, such as EF.
 A tangent can be represented by a line, such as GH.
 An arc can be represented by a curved line, such as HI.
 A sector can be represented by a region of a circle, such as IJK.
 A segment can be represented by a region of a circle, such as KLM.
Applications
The different parts of a circle are used in a variety of applications, such as:
 Geometry: The parts of a circle are used to define and study geometric shapes, such as triangles, quadrilaterals, and polygons.
 Trigonometry: The parts of a circle are used to define and study trigonometric functions, such as sine, cosine, and tangent.
 Calculus: The parts of a circle are used to define and study calculus concepts, such as derivatives and integrals.
 Physics: The parts of a circle are used to define and study physical concepts, such as motion, force, and energy.
 Engineering: The parts of a circle are used to design and build structures, such as bridges, buildings, and machines.
Write down the circle formulas.
Circle Formulas
 Circumference: The circumference of a circle is the distance around the circle. It is calculated by multiplying the diameter of the circle by pi (π), which is approximately 3.14.
$$C = \pi d$$
 Area: The area of a circle is the amount of space enclosed by the circle. It is calculated by multiplying the square of the radius of the circle by pi (π).
$$A = \pi r^2$$

Radius: The radius of a circle is the distance from the center of the circle to any point on the circle.

Diameter: The diameter of a circle is the distance across the circle through the center. It is twice the length of the radius.
$$d = 2r$$
 Sector Area: The area of a sector of a circle is the area of the region bounded by two radii and the intercepted arc. It is calculated by multiplying the central angle of the sector (in radians) by the square of the radius of the circle and then dividing by 2.
$$A = \frac{1}{2}r^2\theta$$
 Arc Length: The arc length of a circle is the distance along the circle between two points. It is calculated by multiplying the central angle of the arc (in radians) by the radius of the circle.
$$s = r\theta$$
Examples:
 A circle with a radius of 5 cm has a circumference of 2π(5) = 10π cm and an area of π(5)^2 = 25π cm^2.
 A sector of a circle with a radius of 10 cm and a central angle of 60 degrees has an area of 1/2(10)^2(60π/180) = 50π/3 cm^2.
 An arc of a circle with a radius of 8 cm and a central angle of 90 degrees has a length of 8(90π/180) = 4π cm.
Define radius and diameter of a circle.
Radius of a Circle:
The radius of a circle is the distance from the center of the circle to any point on the circle. It is a straight line segment that connects the center to a point on the circle. The radius is always positive and is measured in the same units as the length of the circle.
Diameter of a Circle:
The diameter of a circle is the distance across the circle through the center. It is the longest straight line segment that can be drawn inside the circle. The diameter is always twice the length of the radius and is also measured in the same units as the length of the circle.
Examples:
 If a circle has a radius of 5 cm, then the diameter of the circle is 10 cm.
 If a circle has a diameter of 12 m, then the radius of the circle is 6 m.
Applications:
The radius and diameter of a circle are important measurements that are used in many different applications, including:
 Geometry: The radius and diameter are used to calculate the area and circumference of a circle.
 Engineering: The radius and diameter are used to design and build circular objects, such as gears, wheels, and pipes.
 Architecture: The radius and diameter are used to design and build circular structures, such as domes and arches.
 Sports: The radius and diameter are used to design and build sports equipment, such as balls, hoops, and tracks.
Understanding the radius and diameter of a circle is essential for many different fields and applications.
Define chord
Chord
In music, a chord is a group of notes played together. Chords are the building blocks of harmony, and they can be used to create a wide variety of musical textures and effects.
Chords are typically made up of three or more notes, and they are usually played on a keyboard instrument, such as a piano or guitar. The notes in a chord are typically arranged in a specific order, and the intervals between the notes determine the sound of the chord.
There are many different types of chords, and each type has its own unique sound and function. Some of the most common types of chords include:
 Major chords: Major chords are bright and cheerful, and they are often used in happy or uplifting music.
 Minor chords: Minor chords are dark and sad, and they are often used in sad or melancholic music.
 Dominant chords: Dominant chords are tense and unresolved, and they are often used to create a sense of anticipation or suspense.
 Diminished chords: Diminished chords are dissonant and unstable, and they are often used to create a sense of unease or anxiety.
Chords can be used to create a wide variety of musical effects. For example, chords can be used to:
 Create harmony: Chords can be used to create a sense of harmony and balance in a piece of music.
 Add texture: Chords can be used to add texture and interest to a piece of music.
 Create tension and release: Chords can be used to create a sense of tension and release in a piece of music.
 Convey emotion: Chords can be used to convey a wide range of emotions, from happiness to sadness to anger.
Chords are an essential part of music, and they play a vital role in creating the overall sound and feel of a piece of music.
Examples of chords:
 C major chord: The C major chord is made up of the notes C, E, and G.
 A minor chord: The A minor chord is made up of the notes A, C, and E.
 G dominant chord: The G dominant chord is made up of the notes G, B, and D.
 F diminished chord: The F diminished chord is made up of the notes F, A♭, and C♭.
These are just a few examples of the many different types of chords that exist. Each chord has its own unique sound and function, and they can be used to create a wide variety of musical effects.