Calculate Triangle Height: Finding Altitude AD in Triangle ABC

Triangle Heights with Perpendicular Altitude

Given the following triangle:

Write down the height of the triangle ABC.

AAABBBCCCDDD

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Determine the height of the triangle
00:03 The height in a triangle is a perpendicular line from a vertex to the opposite side
00:06 or to the extension of the side
00:09 At the intersection point, the angle between the lines is a right angle (90 degrees)
00:14 This is the solution

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

Given the following triangle:

Write down the height of the triangle ABC.

AAABBBCCCDDD

2

Step-by-step solution

To solve this problem, we need to identify the height of triangle ABC from the diagram. The height of a triangle is defined as the perpendicular line segment from a vertex to the opposite side, or to the line containing the opposite side.

In the given diagram:

  • A A is the vertex from which the height is drawn.
  • The base BC BC is a horizontal line lying on the same level.
  • AD AD is the line segment originating from point A A and is perpendicular to BC BC .

The perpendicularity of AD AD to BC BC is illustrated by the right angle symbol at point D D . This establishes AD AD as the height of the triangle ABC.

Considering the options provided, the line segment that represents the height of the triangle ABC is indeed AD AD .

Therefore, the correct choice is: AD AD .

3

Final Answer

AD

Key Points to Remember

Essential concepts to master this topic
  • Definition: Height is perpendicular segment from vertex to opposite side
  • Identification: Look for right angle symbol (square) at base
  • Verification: Height forms 90° angle with base line ✓

Common Mistakes

Avoid these frequent errors
  • Confusing height with triangle sides
    Don't choose any side like AB or AC as the height = selecting slanted lines! These are sides of the triangle, not perpendicular distances. Always identify the perpendicular line segment marked with a right angle symbol.

Practice Quiz

Test your knowledge with interactive questions

True or false:

DE not a side in any of the triangles.
AAABBBCCCDDDEEE

FAQ

Everything you need to know about this question

How do I know which line is the height?

+

Look for the right angle symbol (small square) where the line meets the base. In this diagram, AD AD has a right angle symbol at point D D , showing it's perpendicular to base BC BC .

Why isn't AB or AC the height?

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Because AB AB and AC AC are the sides of the triangle, not heights. Heights must be perpendicular to the opposite side, while triangle sides are slanted.

Can a triangle have more than one height?

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Yes! Every triangle has three heights - one from each vertex to the opposite side. This problem asks specifically for the height from vertex A A .

What if the height falls outside the triangle?

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In obtuse triangles, some heights can fall outside the triangle. But you still measure the perpendicular distance from the vertex to the extended base line.

Is the height always vertical?

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No! The height is perpendicular to the base, not necessarily vertical. If the base is tilted, the height will be tilted too, but still forms a 90° angle with the base.

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