2010 AMC 10B Problems/Problem 16
Problem
A square of side length and a circle of radius share the same center. What is the area inside the circle, but outside the square?
Solution 1
The radius of the circle is . Half the diagonal of the square is . We can see that the circle passes outside the square, but the square is NOT completely contained in the circle. Therefore the picture will look something like this:
Then we proceed to find: 4 $\cdot (area of sector marked off by the two radii - area of the triangle with sides on the square and the two radii).
First we realize that the radius perpendicular to the side of the square between the two radii marking off the sector splits$ (Error compiling LaTeX. )ABaOX=\frac12a.$<cmath>a^2+\left( \frac12 \right) ^2 = \left( \frac{\sqrt{3}}{3} \right) ^2</cmath>
Solving,$ (Error compiling LaTeX. )a= \frac{\sqrt{3}}{6}2a=\frac{\sqrt{3}}{3}AB=AO=BO\triangle AOB60^{\circ}\pi \left( \frac{\sqrt{3}}{3} \right) ^2 \left( \frac{60}{360} \right) = \frac{\pi}{18}$.
Now we turn to the triangle. Since it is equilateral, we can use the formula for the [[area of an equilateral triangle]] which is
<cmath>\frac{s^2\sqrt{3}}{4} = \frac{\frac13 \sqrt{3}}{4} = \frac{\sqrt{3}}{12}</cmath>
Putting it together, we get the answer to be$ (Error compiling LaTeX. )4 \left( \frac{\pi}{18}-\frac{\sqrt{3}}{12} \right)= \boxed{\textbf{(B)}\ \frac{2\pi}{9}-\frac{\sqrt{3}}{3}}$
Solution 2(Intense Sketch)
After finding the equilateral triangle, you know there is going to be a factor of , so the answer is
See Also
2010 AMC 10B (Problems • Answer Key • Resources) | ||
Preceded by Problem 15 |
Followed by Problem 17 | |
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