Geometry Properties of Trapezoids
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It's a Trap!
Properties of Trapezoids

 

 When we have an object with four sides

 but only two of the sides are parallel
 we call it a TRAPEZOID.
 (Impressive name, eh?)
 

 

 
 Most of the time, the sides of a trapezoid 
 are all different lengths.
 Sometimes the left side and right side
 turn out to be the same length.
 
 To calculate the area of a trapezoid,
 we do something like what we did with the rhombus.
 Here, we cut off a piece from each end.
 Like this ...
 

 

 
 and flip them up to the top of the drawing.
 Like this ...
 

 

 
 Now we have a rectangle,
and that we can deal with. 
 

 

 
 Another way to look at this, 
 is that we chopped off some of the length
 of the long side on the bottom.
 And add those pieces to the short side on the top.
 

 

 
 So that both the top and bottom lengths are the same.
 

 

 
 We can do that with two numbers too!
 We just add them together and divide by two.
 We call that finding the average.
 
 Example:
 Make the top and bottom sides of the trapezoid
 the same length and find that length.
 

 

 
 So great, now the top and bottom sides
 are the same length.
 But we still can't figure out the area of the trapezoid.
 We need to know how far it is
 from the bottom to the top
 (just like with the rhombus)
 That measure is called the height or altitude.
 Say the height of this trapezoid was 4.
 We would get:
 

 

 
 Let's do one more ...
 
 Example:
 Find the area of the trapezoid ...
 

 

 
 1) Add the top and bottom sides together
 and divide by two. That is, find the average ...
 

 

 
 2) Multiply that number times the height.
 

 Area = 6 7

 Area = 42

 

   copyright 2005 Bruce Kirkpatrick

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