2019 AIME I Problem 15
Below is the professionally curated solution for Problem 15 of the 2019 AIME I, from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 2019 AIME I solutions, or check the answer key.
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Difficulty rating: 3500
15.
Let be a chord of a circle and let be a point on the chord Circle passes through and and is internally tangent to Circle passes through and and is internally tangent to Circles and intersect at points and Line intersects at and Assume that and where and are relatively prime positive integers. Find
Solution:
Since lies on both and and internally tangent circles meet only at their point of tangency, is tangent to at likewise is tangent at Let be the intersection of the tangent lines to at and Each tangent line is also tangent to the corresponding inner circle, so the powers of with respect to and are and which are equal. Hence lies on the radical axis and along the line through the last equality because is tangent to
Because the point lies on the perpendicular bisector of if is the midpoint of then Also the power of in gives Set and so The relations become Expanding the second and substituting the first yields and substituting back gives so
Finally so and Therefore
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 I · 2016 AIME II · 2017 AIME I · 2017 AIME II · 2018 AIME I · 2018 AIME II · 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