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The number of square units it takes to exactly fill the interior of a
triangle.
Try this Drag the orange dots on each vertex
to reshape the triangle. The formula shown will recalculate the area using this method.
(If there is no image below, see support page.)
Most common method
Usually called "half of base times height", the area of a triangle is given by the formula below.
where
b is the length of the base
a is the length of the corresponding altitude
See Triangle definition for a definition of base and altitude.
You can choose any side to be the base. The altitude must be the one corresponding to the base you choose.
The altitude is the line perpendicular to the selected base from the opposite vertex.
In the figure above, one side has been chosen as the base and its corresponding altitude is shown.
Methods for finding triangle area
Try this
In the figure above, drag the top of triangle carefully from left to right, but without moving it up or down.
It's a little tricky, but as you drag the vertex, notice that the area does not change.
The area is dependent on the base and height, and neither of them changes as you move the top vertex side-to-side.
Related triangle topics
General
Perimeter / Area
Triangle types
Triangle centers
Congruence and Similarity
Solving triangles
Triangle quizzes and exercises
(C) 2009 Copyright John Page
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