2016 AIME I Problem 15
Below is the professionally curated solution for Problem 15 of the 2016 AIME I, from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 2016 AIME I solutions, or check the answer key.
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Difficulty rating: 3700
15.
Circles and intersect at points and Line is tangent to and at and respectively, with line closer to point than to Circle passes through and intersecting again at and intersecting again at The three points are collinear, and Find
Solution:
Line is the radical axis of and line that of and and line that of and so the three lines meet at the radical center (They cannot be parallel: that would force a symmetric configuration with ) Let The power of with respect to each circle gives so is the midpoint of with between and
Since is cyclic, and since is cyclic, as are collinear these add to so is cyclic. The tangent-chord angle at gives so and symmetrically Hence is a parallelogram, and since is the midpoint of diagonal it is also the midpoint of therefore Moreover and (by the tangent-chord angle at ) so triangles and are similar, giving
Putting it together, which equals
Problem 15 in Other Years
1997 AIME · 1998 AIME · 1999 AIME · 2000 AIME I · 2000 AIME II · 2001 AIME I · 2001 AIME II · 2002 AIME I · 2002 AIME II · 2003 AIME I · 2003 AIME II · 2004 AIME I · 2004 AIME II · 2005 AIME I · 2005 AIME II · 2006 AIME I · 2006 AIME II · 2007 AIME I · 2007 AIME II · 2008 AIME I · 2008 AIME II · 2009 AIME I · 2009 AIME II · 2010 AIME I · 2010 AIME II · 2011 AIME I · 2011 AIME II · 2012 AIME I · 2012 AIME II · 2013 AIME I · 2013 AIME II · 2014 AIME I · 2014 AIME II · 2015 AIME I · 2015 AIME II · 2016 AIME II · 2017 AIME I · 2017 AIME II · 2018 AIME I · 2018 AIME II · 2019 AIME I · 2019 AIME II · 2020 AIME I · 2020 AIME II · 2021 AIME I · 2021 AIME II · 2022 AIME I · 2022 AIME II · 2023 AIME I · 2023 AIME II · 2024 AIME I · 2024 AIME II · 2025 AIME I · 2025 AIME II · 2026 AIME I · 2026 AIME II