Geometry For Dummies
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You can use the right-triangle trick to find the area of a trapezoid. The following trapezoid TRAP looks like an isosceles trapezoid, doesn’t it? Don’t forget — looks can be deceiving.

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You should be thinking, right triangles, right triangles, right triangles. So draw in two heights straight down from R and A as shown in the following figure.

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You can see that QW, like RA, is 14. Then, because TP is 28, that leaves 28 – 14, or 14, for the sum of TQ and WP. Next, you can assign segment TQ a length of x, which gives segment WP a length of 14 – x. Now you’re all set to use — what else? — the Pythagorean Theorem. You have two unknowns, x and h, so to solve, you need two equations:

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Now solve the system of equations. First, you subtract the second equation from the first, column by column:

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Mark Ryan has taught pre-algebra through calculus for more than 25 years. In 1997, he founded The Math Center in Winnetka, Illinois, where he teaches junior high and high school mathematics courses and standardized test prep classes. He also does extensive one-on-one tutoring. He is a member of the Authors Guild and the National Council of Teachers of Mathematics. Ryan is the author of Calculus For Dummies, Calculus Workbook For Dummies, and Geometry Workbook For Dummies.

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