Difference between revisions of "2001 AMC 12 Problems/Problem 8"
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| − | The blue lines will be joined together to form a single blue line on the surface of the cone, hence <math> | + | The blue lines will be joined together to form a single blue line on the surface of the cone, hence <math>10</math> will be the <math>\text{slant height}</math> of the cone. |
The red line will form the circumference of the base. We can compute its length and use it to determine the radius. | The red line will form the circumference of the base. We can compute its length and use it to determine the radius. | ||
| − | The length of the red line is <math>\dfrac{252}{360}\cdot 2\pi \cdot 10 = 14\pi</math>. This is the circumference of a circle with radius <math> | + | The length of the red line is <math>\dfrac{252}{360}\cdot 2\pi \cdot 10 = 14\pi</math>. This is the circumference of a circle with radius <math>7</math>. |
Therefore the correct answer is <math>\boxed{\text{C}}</math>. | Therefore the correct answer is <math>\boxed{\text{C}}</math>. | ||
Revision as of 10:58, 20 October 2020
- The following problem is from both the 2001 AMC 12 #8 and 2001 AMC 10 #17, so both problems redirect to this page.
Problem
Which of the cones listed below can be formed from a 
sector of a circle of radius 
by aligning the two straight sides?
![[asy] import graph; unitsize(1.5cm); defaultpen(fontsize(8pt)); draw(Arc((0,0),1,-72,180),linewidth(.8pt)); draw(dir(288)--(0,0)--(-1,0),linewidth(.8pt)); label("$10$",(-0.5,0),S); draw(Arc((0,0),0.1,-72,180)); label("$252^{\circ}$",(0.05,0.05),NE); [/asy]](http://latex.artofproblemsolving.com/b/b/8/bb8af0c17ff35be1e553d36477a23ce3f026bded.png)
Solution
![[asy] import graph; unitsize(1.5cm); defaultpen(fontsize(8pt)); draw(Arc((0,0),1,-72,180),linewidth(.8pt) + red); draw(dir(288)--(0,0)--(-1,0),linewidth(.8pt) + blue); label("$10$",(-0.5,0),S); draw(Arc((0,0),0.1,-72,180)); label("$252^{\circ}$",(0.05,0.05),NE); [/asy]](http://latex.artofproblemsolving.com/2/1/f/21ff3c1e4bdeb7eae01918390e3702a2b8ab2a01.png)
The blue lines will be joined together to form a single blue line on the surface of the cone, hence will be the 
of the cone.
The red line will form the circumference of the base. We can compute its length and use it to determine the radius.
The length of the red line is 
. This is the circumference of a circle with radius 
.
Therefore the correct answer is 
.
See Also
| 2001 AMC 12 (Problems • Answer Key • Resources) | |
| Preceded by Problem 7 |
Followed by Problem 9 |
| 1 • 2 • 3 • 4 • 5 • 6 • 7 • 8 • 9 • 10 • 11 • 12 • 13 • 14 • 15 • 16 • 17 • 18 • 19 • 20 • 21 • 22 • 23 • 24 • 25 | |
| All AMC 12 Problems and Solutions | |
| 2001 AMC 10 (Problems • Answer Key • Resources) | ||
| Preceded by Problem 16 |
Followed by Problem 18 | |
| 1 • 2 • 3 • 4 • 5 • 6 • 7 • 8 • 9 • 10 • 11 • 12 • 13 • 14 • 15 • 16 • 17 • 18 • 19 • 20 • 21 • 22 • 23 • 24 • 25 | ||
| All AMC 10 Problems and Solutions | ||
The problems on this page are copyrighted by the Mathematical Association of America's American Mathematics Competitions. 
