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A trapezoid is a 2-dimensional geometric figure with four sides, at least one set of which are parallel. The parallel sides are called the bases, while the other sides are called the legs. The term 'trapezium,' from which we got our word trapezoid has been in use in the English language since the 1500s and is from the Latin meaning 'little table.'
There are a few special trapezoids that are worth mentioning.
In an isosceles trapezoid, the legs have the same length and the base angles have the same measure.
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In a right trapezoid, two adjacent angles are right angles.
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If the trapezoid has no sides of equal measure, it is called a scalene trapezoid.
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A parallelogram is a trapezoid with two sets of parallel sides.
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There is actually some controversy over whether a parallelogram is a trapezoid. One group states that the definition of a trapezoid is having only one set of parallel sides, which would exclude the parallelogram because it has two sets of parallel sides. The other, more mainstream group, states that the definition of a trapezoid is having at least one set of parallel sides, which includes the parallelogram. For our discussions, because it is the more widely accepted view, we will consider a parallelogram to be a trapezoid.
The formula for the perimeter of a trapezoid is P = (a + b + c + d). To find the perimeter of a trapezoid, just add the lengths of all four sides together.
The formula for the area of a trapezoid is A = (1/2)(h)(a + b), where:
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An isosceles trapezoid has special properties that do not apply to any of the other trapezoids:
Let's try a couple of practice problems to test your newfound trapezoid knowledge. Feel free to pause the video at any point to work through the problems yourself.
1.) Find the perimeter and area of the following trapezoid:
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To find the perimeter, simply add all four sides together.
P = 12mm + 14mm + 18mm + 13mm = 57mm
To find the area, use the formula A = (1/2)(h)(a + b).
A = (1/2)(11mm)(12mm + 18mm) = 165mm^2
2.) Find the area of the following trapezoid:
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Again, use the area formula A = (1/2)(h)(a + b).
A = (1/2)(6ft)(9ft + 4ft)
A = 39ft^2
A trapezoid is a 2-dimensional figure with four sides. In order for it to be classified as a trapezoid, it must have at least one set of parallel sides. Trapezoids play a key role in architecture and also can be found in numerous everyday items. Take a look at the glass you are drinking from at your next meal. From the side, it's probably shaped like a trapezoid.
Review the video lesson and its corresponding transcript so that you can:
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