Difference between revisions of "1993 AHSME Problems/Problem 14"
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== Solution == | == Solution == | ||
− | <math>\ | + | <asy> |
+ | draw((-1,0)--(1,0)--(1+sqrt(2),sqrt(2))--(0,sqrt(2)+sqrt(13-2*sqrt(2)))--(-1-sqrt(2),sqrt(2))--cycle,black+linewidth(.75)); | ||
+ | draw((1+sqrt(2),sqrt(2))--(-1-sqrt(2),sqrt(2))); | ||
+ | draw((-1,0)--(-1,sqrt(2))); | ||
+ | draw((1,0)--(1,sqrt(2))); | ||
+ | MP("F",(-1,sqrt(2)),N);MP("G",(1,sqrt(2)),N); | ||
+ | MP("A",(-1,0),SW);MP("B",(1,0),SE);MP("C",(1+sqrt(2),sqrt(2)),E);MP("D",(0,sqrt(2)+sqrt(13-2*sqrt(2))),N);MP("E",(-1-sqrt(2),sqrt(2)),W); | ||
+ | dot((-1,0));dot((1,0));dot((1+sqrt(2),sqrt(2)));dot((-1-sqrt(2),sqrt(2)));dot((0,sqrt(2)+sqrt(13-2*sqrt(2)))); | ||
+ | </asy> | ||
+ | |||
+ | First, drop perpendiculars from points <math>A</math> and <math>B</math> to segment <math>EC</math>. | ||
+ | |||
+ | Since <math>\angle EAB = 120^{\circ}</math>, <math>\angle EAF = 30^{\circ}</math>. | ||
+ | |||
+ | This implies that <math>\triangle EAF</math> is a 30-60-90 Triangle, so <math>EF = 1</math> and <math>AF = \sqrt3</math>. | ||
+ | |||
+ | Similarly, <math>GB = \sqrt3</math> and <math>GC = 1</math>. | ||
+ | |||
+ | Since <math>FABG</math> is a rectangle, <math>FG = AB = 2</math>. | ||
+ | |||
+ | Now, notice that since <math>EC = EF + FG + GC = 1+2+1=4</math>, triangle <math>DEC</math> is equilateral. | ||
+ | |||
+ | Thus, <math>[ABCDE] = [EABC]+[DCE] = \frac{2+4}{2}(\sqrt3)+\frac{4^2\cdot\sqrt3}{4} = 3\sqrt3+4\sqrt3=\boxed{7\sqrt3 (B)}</math> | ||
+ | |||
+ | -AOPS81619 | ||
== See also == | == See also == |
Latest revision as of 18:01, 9 March 2020
Problem
The convex pentagon has and . What is the area of ABCDE?
Solution
First, drop perpendiculars from points and to segment .
Since , .
This implies that is a 30-60-90 Triangle, so and .
Similarly, and .
Since is a rectangle, .
Now, notice that since , triangle is equilateral.
Thus,
-AOPS81619
See also
1993 AHSME (Problems • Answer Key • Resources) | ||
Preceded by Problem 13 |
Followed by Problem 15 | |
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All AHSME Problems and Solutions |
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