Difference between revisions of "1998 AHSME Problems/Problem 8"
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The area of the trapezoid is <math>\frac{1}{3}</math>, and the shorter base and height are both <math>\frac{1}{2}</math>. Therefore, <cmath>\frac{1}{3}=\frac{1}{2}\cdot \frac{1}{2}\cdot \left(\frac{1}{2}+x\right) \Rightarrow x=\frac{5}{6}\rightarrow \boxed{\text{D}}</cmath> | The area of the trapezoid is <math>\frac{1}{3}</math>, and the shorter base and height are both <math>\frac{1}{2}</math>. Therefore, <cmath>\frac{1}{3}=\frac{1}{2}\cdot \frac{1}{2}\cdot \left(\frac{1}{2}+x\right) \Rightarrow x=\frac{5}{6}\rightarrow \boxed{\text{D}}</cmath> | ||
+ | |||
+ | == Solution 3 == | ||
+ | |||
+ | Divide the pentagon into 2 small congruent trapezoids by extending the common shorter base of the 2 larger trapezoids. | ||
+ | |||
+ | Since each of the smaller trapezoids has its area half each of the larger trapezoids, and each of them has a base <math>\frac{1}{2}</math>, we have | ||
+ | <cmath>b_{large}+\frac{1}{2}=2(b_{small}+ \frac{1}{2})</cmath> | ||
+ | <cmath>x+\frac{1}{2}=2((1-x)+\frac{1}{2})</cmath> | ||
+ | <cmath>x=\frac{5}{6}\boxed{D}</cmath> | ||
+ | |||
+ | ~ Nafer | ||
== See also == | == See also == | ||
− | {{AHSME box|year=1998|num-b= | + | {{AHSME box|year=1998|num-b=7|num-a=9}} |
[[Category:Introductory Geometry Problems]] | [[Category:Introductory Geometry Problems]] | ||
+ | {{MAA Notice}} |
Latest revision as of 10:28, 2 December 2019
Problem
A square with sides of length is divided into two congruent trapezoids and a pentagon, which have equal areas, by joining the center of the square with points on three of the sides, as shown. Find , the length of the longer parallel side of each trapezoid.
Solution
Solution 1
Then . Let the shorter side of be and the base of be such that ; then implies that , and since it follows that and .
Solution 2
The area of the trapezoid is , and the shorter base and height are both . Therefore,
Solution 3
Divide the pentagon into 2 small congruent trapezoids by extending the common shorter base of the 2 larger trapezoids.
Since each of the smaller trapezoids has its area half each of the larger trapezoids, and each of them has a base , we have
~ Nafer
See also
1998 AHSME (Problems • Answer Key • Resources) | ||
Preceded by Problem 7 |
Followed by Problem 9 | |
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