Difference between revisions of "2006 Cyprus MO/Lyceum/Problem 19"
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==Problem== | ==Problem== | ||
− | + | [[Image:2006 CyMO-19.PNG|250px|right]] | |
− | [[Image:2006 CyMO-19.PNG|250px]] | ||
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− | In the figure, <math>AB \Gamma</math> is an isosceles triangle with<math> AB=A\Gamma=\sqrt2</math> and <math>\ | + | In the figure, <math>AB\Gamma</math> is an [[isosceles triangle]] with<math> AB=A\Gamma=\sqrt2</math> and <math>\angle A=45^\circ</math>. If <math>B\Delta</math> is an [[altitude]] of the [[triangle]] and the [[sector]] <math>B\Lambda \Delta KB</math> belongs to the circle <math>(B,B\Delta )</math>, the [[area]] of the shaded region is |
− | + | <math>\mathrm{(A)}\ \frac{4\sqrt3-\pi}{6}\qquad\mathrm{(B)}\ 4\left(\sqrt2-\frac{\pi}{3}\right)\qquad\mathrm{(C)}\ \frac{8\sqrt2-3\pi}{16}\qquad\mathrm{(D)}\ \frac{\pi}{8}\qquad\mathrm{(E)}\ \text{None of these}</math> | |
− | B | + | ==Solution== |
− | + | <math>A \Delta B</math> is a [[right triangle]] with an angle of <math>45^{\circ}</math>, so it is a <math>45-45-90</math> triangle with <math>B\Delta = \frac{AB}{\sqrt{2}} = 1</math>. | |
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− | + | The area of the entire circle is <math>(1)^2\pi = \pi</math>. The central angle of the sector is <math>\frac{180-45}{2} = \frac{135}{2}</math>, so the area is <math>\frac{\frac{135}{2}}{360}\pi = \frac{3}{16}\pi</math>. | |
− | + | The area of the entire triangle is <math>\frac{1}{2}bh = \frac{\sqrt{2}}{2}</math>. Thus, the answer is <math>\frac{\sqrt{2}}{2} - \frac{3}{16}\pi = \frac{8\sqrt{2} - 3\pi}{16} \Longrightarrow \mathrm{(C)}</math>. | |
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==See also== | ==See also== |
Latest revision as of 22:44, 22 December 2016
Problem
In the figure, is an isosceles triangle with and . If is an altitude of the triangle and the sector belongs to the circle , the area of the shaded region is
Solution
is a right triangle with an angle of , so it is a triangle with .
The area of the entire circle is . The central angle of the sector is , so the area is .
The area of the entire triangle is . Thus, the answer is .
See also
2006 Cyprus MO, Lyceum (Problems) | ||
Preceded by Problem 18 |
Followed by Problem 20 | |
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