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Area of a Triangle

Author:Mikki Becker, cwinske, GeoGebra Materials Team
Topic:Area
In this activity, you will find the area of triangles. First, we will start with right triangles. Move the sliders so your triangle has a base of 7 units and a height of 4 units.

Then, move the slider that says "slide me." What shape did you create?

Select all that apply
  • A
  • B
  • C
  • D
Check my answer (3)

What is the area of the new shape you created?

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Since we our new shape is made of two of the original triangles, what is the area of just one triangle?

Check my answer
Nice work! Let's try another one. Move the base and height sliders so your triangle has a base of 3 units and a height of 10 units.

Move the "slide me" slider. What is the area of the rectangle that was created?

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What is the area of the triangle?

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Nice! Let's try one more right triangle. Move the sliders so the base is 5 units and the height is 5 units, then move the "slide me" slider.

What is the area of the triangle?

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Describe the process to find the area of a right triangle.

Now, we are going to explore finding the area of other types of triangles. Move the base and height sliders below to create an acute triangle that has a base of 5 and a height of 6.

Then, move the "slide me" slider. What shape was created?

Select all that apply
  • A
  • B
  • C
  • D
Check my answer (3)

What is the area of the new shape?

Check my answer

Since that shape is made of two copies of the original triangle, what is the area of just one of the triangles?

Check my answer
Awesome! Let's try another one. Move the base and height sliders so the triangle has a base of 8 and a height of 2. Then move the vertex labeled "D" to create an obtuse triangle.

Then, move the "slide me" slider. What is the area of the parallelogram?

Check my answer

What is the area of the triangle?

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Great thinking! Let's try another one. Move the base and height sliders so the triangle has a base of 9 and a height of 7. Then move the vertex labeled "D" to create an acute triangle, and move the "slide me" slider.

What is the area of the triangle?

Check my answer
Create your own obtuse triangle that you have not created yet.

Describe your triangle and what you found the area to be.

How do you find the area of any triangle with a base "b" and a height "h"? Does this process depend on the type of angles in the triangle?

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