Difference between revisions of "2009 AMC 10B Problems/Problem 16"
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Revision as of 12:54, 4 July 2013
Problem
Points and
lie on a circle centered at
, each of
and
are tangent to the circle, and
is equilateral. The circle intersects
at
. What is
?
Solution
Solution 1
As is equilateral, we have
, hence
. Then $\angla AOC = 120^\circ$ (Error compiling LaTeX. Unknown error_msg), and from symmetry we have
. Finally this gives us
.
We know that , as
lies on the circle. From
we also have
, Hence
, therefore
, and
.
Solution 2
As in the previous solution, we find out that . Hence
and
are both equilateral.
We then have , hence
is the incenter of
, and as
is equilateral,
is also its centroid. Hence
, and as
, we have
, therefore
, and as before we conclude that
.
See Also
2009 AMC 10B (Problems • Answer Key • Resources) | ||
Preceded by Problem 15 |
Followed by Problem 17 | |
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 |
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