Circumscribe

Sally works at "The Pentagon" building. Every morning she has to travel to different blocks to address the employees. She normally takes a circular path as her route.

pentagon circumscribe

Can you relate the concept of the "Circumscribe" to the path Sally takes every morning with respect to the Pentagon?

In this chapter, we will learn about the circumscribe in a circle, circumscribe definition, circumscribed and inscribed, circumscribed triangle along with the concept of circumscribe. 

Check out the interactive examples to know more about the lesson and try your hand at solving a few interesting practice questions at the end of the page.

Lesson Plan

What is Meant by Circumscribe?

According to Merriam-Webster, the meaning of circumscribe or circumscribing is to construct or be constructed around (a geometrical figure) so as to touch as many points as possible.

So any figure that circumscribes any other figure, means it is drawn outside another figure.

But the circumscribing figure must touch all the vertices of the inside figure.

For example, if a circle circumscribes a pentagon, it must touch all the 5 vertices of the pentagon.

circumscribe

Circle circumscribing pentagon


Explain Different Circumscribed Shapes 

Any shape can circumscribe any other shape. 

Circumscribed Shapes

Here are few circumscribed shapes with their illustrations:

Circumscribed Circle

The circumscribed circle is the circle drawn outside of any other shapes such as polygon, touching all the vertices of the polygon, and is termed as circumcircle.

circumscribe

Circle circumscribing triangle

Note: All 3 vertices have been touched by the circle.

Circumscribed Triangle

The circumscribed triangle is the triangle drawn outside of any other shapes. It must be touching all the vertices, if available.

circumscribe

Triangle circumscribing square

Circumscribed Pentagon

The circumscribed pentagon is the pentagon drawn outside of any other shapes. It must be touching all the vertices, if available.

Pentagon can be regular or irregular.

pentagon circumscribe

Pentagon circumscribing circle

Circumscribed Angle

The circumscribed angle is drawn when the arms of the angle touch the circle as tangents are drawn to the circle.

circumscribe

Angle circumscribing circle

Circumscribed Quadrilateral

The circumscribed quadrilateral is the quadrilateral drawn outside of any other shapes. It must be touching all the vertices, if available.

circumscribe

Quadrilateral circumscribing triangle

Circumscribed Hexagon

The circumscribed quadrilateral is the quadrilateral drawn outside of any other shapes. It must be touching all the vertices, if available.

circumscribe

Hexagon circumscribing circle

Circumscribed Rectangle

The circumscribed rectangle is the rectangle drawn outside of any other shapes. It must be touching all the vertices, if available.

circumscribe

Rectangle circumscribing triangle


What Is a Circumscribed Angle?

If we see an ice cream cone in 2D, we can see that the circular shape of the ice cream is perfectly fitting the cone's two sides.

circumscribe

The angle between the sides of the cone is known as the circumscribed angle.

The circumscribed angle is drawn when the arms of the angle touch the circle as tangents are drawn to the circle.

circumscribe

Example

Here is another example to relate to circumscribed angles in real life:

Football Trophies

circumscribe


 
important notes to remember
Important Notes
  1. Not all quadrilaterals are circumscribed quadrilaterals.

  2. If any shape is circumscribing any other shape, it must be touching all the vertices, if available.

  3. The inscribed and circumscribed figure are complementary terms. An inscribed figure is that shape that is drawn inside another shape while a shape drawn outside another shape is referred to as a circumscribed shape.

Solved Examples

Example 1

 

 

Nora wants to put a square curtain of each side 14 \( \text{in}\), completing enclosing her circular window.

Can you help her calculate the area of the inscribed circle?

Put Shutter on window

Solution

Each side of the square curtain = 14 \( \text{in}\)

Radius of circle = \( \frac{14}{2} = 7\) \( \text{in}\)

Area of circle = \( \pi \times r^2\)

Thus, area of the circular window,

\( \begin{align*} \text {Area}  &= \pi \times r^2 \\ &= \frac{22}{7} \times 7^2 = 154 \ \text {square in} \end{align*} \) 

\( \therefore \text {Area} = 154 \ \text {square in}\)
Example 2

 

 

Lucy is solving the following question:

A quadrilateral \( \text {ABCD}\) is inscribed in a circle as shown in the figure.

Can you help her determine the unknown angles?

Circumscribe solved example

Solution

We know,

For a quadrilateral inscribed in a circle, the sum of opposite sides = \( 180^\circ \)

Therefore,

\( \begin{align*} \angle A + \angle C &= 180^\circ \\ \angle 78^\circ +  \angle C &= 180^\circ \\  \angle C &= 180^\circ - \angle 78^\circ \\ \angle C &= 102^\circ \end{align*} \)

Similarly,

\( \begin{align*} \angle B + \angle D &= 180^\circ \\ \angle 105^\circ +  \angle D &= 180^\circ \\  \angle D &= 180^\circ - \angle 105^\circ \\ \angle D &= 75^\circ \end{align*} \)

\( \therefore \begin{align*} \angle C &= 102^\circ \\  \angle D &= 75^\circ \end{align*}  \)
Thinking out of the box
Think Tank
  • How will you construct a triangle inside a circumscribed circle?

Interactive Questions 

Here are a few activities for you to practice.

Select/type your answer and click the "Check Answer" button to see the result.

 
 
 
 

Let's Summarize 

The mini-lesson targeted the fascinating concept of circumscribe. The math journey around the circumscribe formula starts with what a student already knows, and goes on to creatively crafting a fresh concept in the young minds. Done in a way that not only it is relatable and easy to grasp, but also will stay with them forever. Here lies the magic with Cuemath.

About Cuemath

At Cuemath, our team of math experts is dedicated to making learning fun for our favorite readers, the students!

Through an interactive and engaging learning-teaching-learning approach, the teachers explore all angles of a topic.

Be it worksheets, online classes, doubt sessions, or any other form of relation, it’s the logical thinking and smart learning approach that we, at Cuemath, believe in.


Frequently Asked Questions (FAQs)

1. What is the difference between circumscribed and inscribed?

An inscribed figure is that shape that is drawn inside another shape.

A shape drawn outside another shape is referred to as a circumscribed shape. 

2. How do you find the radius of a circumscribed circle?

The radius of a circumscribed circle can be calculated by comparing the dimensions of both the inscribed figure and the circumscribed circle.

3. What is an inscribed circle?

An inscribed circle is the circle that is drawn inside any other figure.

  
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