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# Angle Sum Property of a Quadrilateral

• Last Updated : 13 Mar, 2023

Quadrilaterals are encountered everywhere in life, every square rectangle, any shape with four sides is a quadrilateral. We know, three non-collinear points make a triangle. Similarly, four non-collinear points take up a shape that is called a quadrilateral. It has four sides, four angles, and four vertices.

Both the figures above are examples of quadrilaterals. ABCD is a quadrilateral. AB, BC, CD, and DA are the four sides of the quadrilateral. A, B, C, and D are four vertices, and âˆ A, âˆ B, âˆ C, and âˆ D are the angles of this quadrilateral. Before coming to the Angle Sum Property of Quadrilateral we have to know some basic terminologies of quadrilateral, which are discussed below in the article.

### Some Important Terminology

Let’s look at some terms and conventions related to quadrilaterals.

Opposite Sides: Two Sides of the quadrilateral are called opposite sides if they have no common vertex.

For example: In the figure given above look at the quad ABCD. Here, AB and CD are opposite sides. Similarly, AD and BC are opposite sides.

Opposite Angles: Two angles of a quadrilateral are opposite if they don’t have any common arm.

For example: In the figure ABCD again, angle A and angle C don’t have any common arm. Thus, they can be considered as opposite angles. Similarly, angles B and D are also opposite angles.

Adjacent Sides: Two sides are called adjacent if sides have a common vertex.

For example: AB and AD have common vertex “A”. So, they are called adjacent sides. Similarly, AB, BC; BC, CD and AD, DC are adjacent sides.

Adjacent Angles: Two angles, if they have a common arm are called adjacent angles.

For example: âˆ A, âˆ B are adjacent angles.

Example: List the pair of opposite sides and adjacent angles from the quadrilateral given below.

Solution:

Pair of opposite sides are the sides which don’t have any common vertices.

So, in this case (AB, CD) and (AC, BD) are two pairs of opposite sides.

Similarly, going by the definition given above. Pair of adjacent sides are,

(AC, AB); (AB, BD); (BD, DC); (CD, AC)

## Angle Sum Property of Quadrilateral

This property states that the sum of all angles of a quadrilateral is 360Â°. Let’s prove this.

### Theorem: Sum of all four angles of a quadrilateral is 360Â°.

Proof:

Join AC.

Now notice,

âˆ 1 + âˆ 2 = âˆ A

âˆ 3 + âˆ 4 = âˆ C

Therefore, from triangle ABC

âˆ 4 + âˆ 2 + âˆ B = 180o

âˆ 3 + âˆ 1 + âˆ D = 180o

âˆ 4 + âˆ 2 + âˆ B + âˆ 3 + âˆ 1 + âˆ D = 360o

(âˆ 1 + âˆ 2) + (âˆ 3+ âˆ 4) + âˆ B + âˆ D = 360o

âˆ A + âˆ C + âˆ B + âˆ D = 360o

Thus, this proves that sum of all interior angles of a quadrilateral is 360Â°.

Quadrilateral is a polygon which has four sides and four angles. According to the angle sum property of a quadrilateral, the sum of its interior angles is 360 degrees. This property is very useful for finding the unknown angle of the quadrilateral. Suppose three angles âˆ A, âˆ B, and âˆ C of any quadrilateral then angle âˆ D can easily be calculated as âˆ D = 360Â° – (âˆ A +âˆ B + âˆ C)

Sum of all the angles of Quadrilateral âˆ A +âˆ B + âˆ C + âˆ D = 360Â°

### Do Sum of Opposite Angles in a Quadrilateral equal 180 Degrees?

Not necessarily, the sum of the opposite angles of any cyclic quadrilateral is supplementary i.e. their sum is 180Â°. But, this is only true for cyclic quadrilaterals, and not all quadrilaterals are cyclic. Hence, we can not say that some of the opposite angles of a quadrilateral equal 180 degrees. But, it is safe to say that sum of the opposite angles in a cyclic quadrilateral is supplementary, i.e. their sum is 180 degrees.

Quadrilaterals can be generally classified into five types:

• Parallelogram: It is quadrilateral which has its opposite sides parallel and congruent to each other. The opposite angles are also equal.
• Rectangle: It is a quadrilateral that has its opposite sides equal and all the angles are at the right angle(90Â°).
• Square: It is a quadrilateral that has all its sides of equal length and all the angles are at the right angle(90Â°).
• Rhombus: It is a parallelogram that has all of its sides of equal length.
• Trapezium: It has one pair of parallel sides. Its sides may or may not be of equal length.

Also, Check

## Solved Examples on Angle Sum Property of Quadrilateral

Example 1: The angles of a quadrilateral are 60Â°, 90Â°, and 90Â°. Find the fourth remaining angle.

Solution:

We know from the angle sum property that the sum of the angles of a quadrilateral are 360o

Let the fourth angle be denoted by “x”.

So,

60Â° + 90Â°+ 90Â° + x = 360Â°

180Â° + 60Â° + x = 360Â°

240Â° + x = 360Â°

x = 120Â°

Example 2: The angles of a quadrilateral are given to be (3x)Â°, (3x + 30)Â°, (6x + 60)Â°, and 90Â°. Find the value of all the angles of quadrilaterals.

Solution:

We know, sum of all the angles of quadrilateral are 360Â°.

3x + (3x + 30) + (6x + 60) + 90 = 360

(3x + 3x + 6x) + (30 + 60 + 90) = 360

(12x) + (180) = 360

12x = 360 â€“ 180

12x = 180

x = 15Â°

Thus, the angles are 45Â°, 75Â°, 150Â° and 90Â°

Example 3: If the angles of a quadrilateral are in the ratio 1: 2: 3: 4, Find the value of the largest angle of that quadrilateral.

Solution:

Since the sum of all 4 angles of a quadrilateral is 360Â°, we can equate the values (by multiplying with a constant) of these ratios to 360Â°

Suppose the constant that is getting multiplied is ‘x’

We can write, x+ 2x+ 3x+ 4x = 360

10x = 360

x = 36Â°

Therefore, the largest angle will be 4x = 4Ã—36 = 144Â°

Example 4: For a trapezium ABCD, âˆ A = 100Â°, âˆ C = 80Â°, Find the rest of the angles.

Solution:

We already know, In a Trapezium, two opposite sides are parallel to each other, here, AB is parallel to CD

Interior angles formed by two parallel lines have a sum of 180Â°(Property of parallel lines)

Therefore, we can write, âˆ A + âˆ D = 180Â°

100Â° + âˆ D = 180Â°

âˆ D = 80Â°

Similarly, âˆ B+ âˆ C = 180Â°

âˆ B + 80Â° = 180Â°

âˆ B = 100Â°

Example 5: In the figure below, the interior angles of the quadrilateral are given as,

âˆ ABC = 50Â°, âˆ BAD = 20Â°, âˆ BCD = 10Â°

Find the value of the exterior angle âˆ ADC.

Solution:

In a quadrilateral, the sum of all the interior angles is 360Â°

âˆ ABC + âˆ BAD + âˆ BCD + âˆ ADC = 360Â°

50Â° + 20Â° + 10Â° + âˆ ADC = 360Â°

The angle that came out is the interior angle, the sum of interior angle and the exterior angle will be 360,

Exterior angle âˆ ADC = 360 â€“ 280 = 80Â°

Example 6: In the given parallelogram ABCD, the value of an interior angle is 60Â°. Find the values of all other angles.

Solution:

The value of âˆ D is given to be 60Â°. We need to find other angles.

We know that sum of adjacent angles in a parallelogram is 180Â°. So let the value of âˆ A be x.

x + 60Â° =180Â°

x = 120Â°

âˆ A = 120Â°

We also know that opposite angles in a parallelogram are equal.

So,

âˆ A = âˆ C and âˆ D = âˆ B

So, âˆ A = 120Â°, âˆ B = 60Â°, âˆ C = 120Â° and âˆ D = 60Â°

Example 7: In the given quadrilateral, âˆ A = 2xÂ°, âˆ B = xÂ°, âˆ C = 90Â° and âˆ D = 3xÂ°. Find the value of the largest angle.

Solution:

We know that by the angle sum property, sum of all the interior angles of a quadrilateral is 360o

So, âˆ A + âˆ B + âˆ C + âˆ D = 360Â°

Given that âˆ C = 90Â°

Let’s plug in the rest of the values given,

2x + x + 90 + 3x = 360

6x = 360 â€“ 90

6x = 270

x = 45Â°

So, the largest angle is âˆ D = 3x = 3(45) = 135Â°

## FAQs on Quadrilateral: Angle Sum Property

### Question 2: What is the angle sum property of a Concave Quadrilateral?

For, a Concave Quadrilateral the angle sum property states that the sum of all the interior angles of a quadrilateral sums up to 360Â°.

### Question 2: What is the angle sum property of a Convex Quadrilateral?

Similarly in a Convex Quadrilateral, the angle sum property states that the sum of all the interior angles of a quadrilateral sums up to 360Â°.

### Question 3: Are opposite angles of a quadrilateral supplementary?

No, the opposite angles in all the quadrilaterals are not supplementary. But in the case of cyclic quadrilateral opposite angles are supplementary.

### Question 4: What is the Sum of within Angles of a Quadrilateral?

According to the angle sum property of the quadrilateral, the sum of all the interior angles of a quadrilateral is 360Â°.