Exterior Angles of Triangles Practice Problems & Solutions

Master exterior angle theorems with step-by-step practice problems. Learn to find missing angles using the exterior angle property of triangles.

📚Practice Exterior Angle Problems and Build Your Confidence
  • Apply the exterior angle theorem to find missing interior angles
  • Calculate exterior angles using the sum of non-adjacent interior angles
  • Solve problems involving supplementary relationships between adjacent angles
  • Work with right triangles and exterior angle properties
  • Use the 360° sum property of all exterior angles
  • Practice both direct calculation and algebraic methods

Understanding Exterior angles of a triangle

Complete explanation with examples

Exterior angles of a triangle

The exterior angle of a triangle is the one that is found between the original side and the extension of the side.

Key Properties:

  • The exterior angle is equal to the sum of the two interior angles of the triangle that are not adjacent to it.
  • Each exterior angle is supplementary to its adjacent interior angle, meaning their sum is 180180^\circ.
  • The sum of all exterior angles of a triangle is always 360360^\circ, no matter the shape of the triangle.

It is defined as follows:

α=A+Bα=∢A+∢B

A1 - Exterior angle of a triangle

Detailed explanation

Practice Exterior angles of a triangle

Test your knowledge with 62 quizzes

Indicates which angle is greater

Examples with solutions for Exterior angles of a triangle

Step-by-step solutions included
Exercise #1

Is DE side in one of the triangles?
AAABBBCCCDDDEEE

Step-by-Step Solution

Since line segment DE does not correspond to a full side of any of the triangles present within the given geometry, we conclude that the statement “DE is a side in one of the triangles” is Not true.

Answer:

Not true

Video Solution
Exercise #2

Determine the type of angle given.

Step-by-Step Solution

To solve this problem, we'll follow these steps:

  • Step 1: Examine the diagram presented.
  • Step 2: Identify any familiar angle formations or configurations.
  • Step 3: Use knowledge of angles to classify the type shown.
  • Step 4: Determine the correct response from available options.

Observing the diagram:

The diagram includes two lines, one horizontal and the other vertical, extending fully. This horizontal extent along with the linear continuation suggests it forms an angle at the intersection with 180180^\circ. This indicates a straight angle.

We classify straight angles because an angle formed by two lines directly facing opposite directions is known to measure 180180^\circ. This diagrammatic representation aligns perfectly to confirm it calculates and visually shows a straight angle.

Thus, by recognizing these details within the diagram, we confirm the type of angle as Straight.

Answer:

Right

Video Solution
Exercise #3

Determine the type of angle given.

Step-by-Step Solution

The problem involves classifying the angle represented visually, which looks like a semicircle with a central axis drawn. This indicates an angle that spans half a complete circle.

A complete circle measures 360360^\circ, so half of it, represented by a semicircle, measures half of 360360^\circ, which is 180180^\circ.

The four primary classifications for angles are:

  • Acute: Less than 9090^\circ
  • Right: Exactly 9090^\circ
  • Obtuse: Greater than 9090^\circ but less than 180180^\circ
  • Straight: Exactly 180180^\circ

Since the angle measures exactly 180180^\circ, it is classified as a straight angle.

Therefore, the type of angle given is Straight.

Answer:

Straight

Video Solution
Exercise #4

Is the straight line in the figure the height of the triangle?

Step-by-Step Solution

The task is to determine whether the line shown in the diagram serves as the height of the triangle. For a line to be considered the height (or altitude) of a triangle, it needs to be a perpendicular segment from a vertex to the line that contains the opposite side, often referred to as the base.

Let's analyze the diagram:

  • The triangle is described by its vertices, forming a shape, and one side is the base. There's a line drawn from one vertex directed toward the opposite side.
  • To be the height, this line must be perpendicular to the side it meets (the base).
  • Though the figure does not explicitly show perpendicularity with a right angle mark, the line appears as a straight, direct connection from the vertex to the base. This is typically indicative of it being a height.
  • Assuming typical geometric conventions and the common depiction of heights in diagrams, the line shows properties consistent with being perpendicular to the opposite side, thereby functioning as the height.

Based on the analysis, the line is indeed the height of the triangle. Thus, the answer is Yes.

Therefore, the solution to the problem is Yes.

Answer:

Yes

Video Solution
Exercise #5

Is the straight line in the figure the height of the triangle?

Step-by-Step Solution

To determine if the straight line in the figure is the height of the triangle, we must verify the following:

  • The line segment must extend from a vertex of the triangle and be perpendicular to the opposite side (or its extension).

In examining the figure provided, we notice that the triangle is formed by vertices at points A,B, A, B, and C C . Let's assume the base is the line segment BC \overline{BC} .

The line in question extends from a vertex A A and appears to intersect the base BC BC at a right angle.

  • Since it is extending from vertex to the opposite side and forming a right angle with it, this line meets the definition of an altitude.

Therefore, the line in the figure is indeed the height of the triangle. By confirming the perpendicular relationship, we determine that this geometric feature correctly describes an altitude.

Yes, the straight line in the figure is the height of the triangle.

Answer:

Yes

Video Solution

Frequently Asked Questions

What is the exterior angle theorem for triangles?

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The exterior angle theorem states that an exterior angle of a triangle equals the sum of the two non-adjacent interior angles. For example, if angles A and B are 50° and 30°, the exterior angle at vertex C would be 80°.

How do you find an exterior angle of a triangle step by step?

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To find an exterior angle: 1) Identify the two interior angles that are NOT adjacent to the exterior angle, 2) Add these two angles together, 3) The sum equals the exterior angle. Alternatively, subtract the adjacent interior angle from 180°.

What is the sum of all exterior angles of a triangle?

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The sum of all three exterior angles of any triangle is always 360°, regardless of the triangle's shape or size. This is a fundamental property that applies to all triangles.

How are exterior and interior angles of triangles related?

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An exterior angle and its adjacent interior angle are supplementary, meaning they add up to 180°. The exterior angle also equals the sum of the two remote (non-adjacent) interior angles.

What are common mistakes when solving exterior angle problems?

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Common errors include: confusing which angles are adjacent vs. non-adjacent, forgetting that exterior and adjacent interior angles sum to 180°, and incorrectly identifying which angle is actually the exterior angle.

Can you use exterior angles to find interior angles of triangles?

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Yes! If you know an exterior angle, you can find interior angles by: 1) Subtracting from 180° to get the adjacent interior angle, or 2) Using the exterior angle theorem if you know one of the non-adjacent interior angles.

Do exterior angle rules work for all types of triangles?

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Yes, the exterior angle theorem applies to all triangles - acute, right, obtuse, scalene, isosceles, and equilateral. The relationships between exterior and interior angles remain consistent regardless of triangle type.

How do you identify an exterior angle in a triangle diagram?

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An exterior angle is formed between one original side of the triangle and the extension of an adjacent side. It lies outside the triangle and is supplementary to the interior angle at the same vertex.

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