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A trapezoid has two parallel sides |
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| and two not parallel sides. | ||
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| If we draw another line inside the trapezoid | ||
| half way between the top and bottom lines. | ||
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| This line will cut the sides on the left and right | ||
| exactly in half. | ||
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| Now try this ... | ||
| Draw a line inside the trapezoid | ||
| one third of the way down from the top line | ||
| to the bottom line. | ||
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| Because 1/3 is EXACTLY half as big as 2/3. | ||
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| Since the side on the left | ||
| and the side on the right are not parallel, | ||
| one can be really long and the other can be really short. | ||
| In any case, the lengths on the left | ||
| will usually not be the same as the lengths on the right. | ||
| Example: | ||
| Find the unknown lengths in the trapezoid. | ||
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| The two pieces of the side on the left | ||
| are the same length as each other. | ||
| That means the two pieces on the right side | ||
| are the same length as each other. | ||
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So the unknown length is 5 |
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| Example: | ||
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Find the unknown length |
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| The side piece on the top left | ||
| is half as long as the side piece on the bottom left. | ||
| That means the unknown side piece on the top right | ||
| is half as long as the side piece on the bottom right. | ||
| The bottom right piece is 8 units long | ||
| so the unknown top right piece is 4 units long. | ||
| The rule we can use with these problems is: | ||
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| With this little rule, we can figure out | ||
| the missing side piece of any trapezoid. | ||
| Example: | ||
| Find the length of the unknown side piece ... | ||
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| Math people LOVE to use "X" for values they don't know. | ||
| Using X, we can write ... | ||
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| We want to get X all by itself. | ||
| Multiply both sides by 15/1 ... | ||
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| Simplify ... | ||
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copyright 2005 Bruce Kirkpatrick |
