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More Geometry Lessons

In these lessons, we will learn

**What is a Cyclic Quadrilateral?**

**Properties of a Cyclic Quadrilateral**

**How to use the properties of a cyclic quadrilateral to find missing angles?**

*ABC* = 90˚ ( angle of semicircle )

∠*ABD* + ∠*DBC* = ∠*ABC*

∠*ABD* + 36˚ = 90˚

∠*ABD* = 54˚

∠*ABD* + *x* = 180˚ ( interior opposite angles of a cyclic quadrilateral)

* x* = 180˚ – 54˚ = 126˚

**How to find missing angles using the properties of a cyclic quadrilateral?**

Opposite angles in a cyclic quadrilateral adds up to 180˚.

Interior opposite angles are equal to their corresponding exterior angles.

Find the missing angles using central and inscribed angle properties.

Can you find the relationship between the missing angles in each figure?**Circle theorems - Alternate segment theorem and Cyclic quadrilaterals**

Exam Practice Question Example:

ABCD is a cyclic quadrilateral within a circle centre O. XY is the tangent to the circle at A.

Angle XAB = 58°, Angle BAD = 78°, Angle DBC = 34°. Prove that AB is parallel to CD.**Proof for the Cyclic Quadrilateral**

This video shows how to prove that opposite angles in a cyclic quadrilateral are supplementary.

It is based on the theorem: Angle at the center is twice angle at the circumference.**Circle Geometry: Cyclic Quadrilateral**

What is the relationship between the angles of a quadrilateral that is inscribed in a circle?

This video shows how to prove that opposite angles in a cyclic quadrilateral are supplementary.

You can use the free Mathway calculator and problem solver below to practice Algebra or other math topics. Try the given examples, or type in your own problem and check your answer with the step-by-step explanations.

More Geometry Lessons

In these lessons, we will learn

- what is a cyclic quadrilateral.
- the properties of a cyclic quadrilateral
- the opposite angles of a cyclic quadrilateral are supplementary.
- the exterior angle of a cyclic quadrilateral is equal to the interior opposite angle.

- to prove that the opposite angles of a cyclic quadrilaterals are supplementary.

A cyclic quadrilateral is a quadrilateral with 4 vertices on the circumference of a circle.

The following diagram shows a cyclic quadrilateral and its properties. Scroll down the page for more examples and solutions.

Cyclic quadrilaterals are also called inscribed quadrilaterals or chordal quadrilaterals.**Property 1: In a cyclic quadrilateral, the opposite angles are supplementary i.e. they add up to 180˚. **

* a* + *c* = 180 ˚**, ***b* + *d* = 180 ˚

**Property 2: The exterior angle of a cyclic quadrilateral is equal to the interior opposite angle. **

* Example: *

The exterior angle ∠* ADF* is equal to the corresponding interior angle ∠* ABC.
*The exterior angle ∠

* Example: *

*AC* is a diameter of the circle. Find the value of *x*.

* Solution: *

∠

∠

∠

∠

* Example: *

Find the values of *x* and *y* in the following figure.

* Solution: *

* x* = 98˚ ( Corresponding opposite angles of a cyclic quadrilateral )

*y* + 27˚ = 53˚ (Corresponding opposite angles of a cyclic quadrilateral)

*y* = 26˚

**Using the properties of a cyclic quadrilateral to find missing angles**

A quadrilateral is cyclic when its four vertices lie on a circle.

Opposite angles in a cyclic quadrilateral adds up to 180˚.

Opposite angles in a cyclic quadrilateral adds up to 180˚.

Interior opposite angles are equal to their corresponding exterior angles.

Find the missing angles using central and inscribed angle properties.

Can you find the relationship between the missing angles in each figure?

Exam Practice Question Example:

ABCD is a cyclic quadrilateral within a circle centre O. XY is the tangent to the circle at A.

Angle XAB = 58°, Angle BAD = 78°, Angle DBC = 34°. Prove that AB is parallel to CD.

This video shows how to prove that opposite angles in a cyclic quadrilateral are supplementary.

It is based on the theorem: Angle at the center is twice angle at the circumference.

What is the relationship between the angles of a quadrilateral that is inscribed in a circle?

This video shows how to prove that opposite angles in a cyclic quadrilateral are supplementary.

Rotate to landscape screen format on a mobile phone or small tablet to use the **Mathway** widget, a free math problem solver that **answers your questions with step-by-step explanations**.

You can use the free Mathway calculator and problem solver below to practice Algebra or other math topics. Try the given examples, or type in your own problem and check your answer with the step-by-step explanations.

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