Difference between revisions of "2023 AIME II Problems/Problem 9"
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− | Notice that line <math>overline{PQ}</math> is the radical axis of circles <math> | + | Notice that line <math>\overline{PQ}</math> is the radical axis of circles <math>\omega_1</math> and <math>\omega_2</math>. By the radical axis theorem, we know that the tangents of any point on line <math>\overline{PQ}</math> to circles <math>\omega_1</math> and <math>\omega_2</math> are equal. Therefore, line <math>\overline{PQ}</math> must pass through the midpoint of <math>\overline{AB}</math>, call this point M. In addition, we know that <math>AM=MB=6</math> by circle properties and midpoint definition. |
Then, by Power of Point, | Then, by Power of Point, | ||
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</cmath> | </cmath> | ||
− | Call the intersection point of line <math>overline{ | + | Call the intersection point of line <math>\overline{A\omega_1}</math> and <math>\overline{XY}</math> be C, and the intersection point of line <math>\overline{B\omega_2}</math> and <math>\overline{XY}</math> be D. <math>ABCD</math> is a rectangle with segment <math>MP=4</math> drawn through it so that <math>AM=MB=6</math>, <math>CP=5</math>, and <math>PD=7</math>. Dropping the altitude from <math>M</math> to <math>overline{XY}</math>, we get that the height of the rectangle is <math>\sqrt{15}</math>. Therefore the area of trapezoid <math>XABY</math> is <math>frac{1}{2}\cdot(12+24)\cdot(\sqrt{15})</math> |
== See also == | == See also == | ||
{{AIME box|year=2023|num-b=8|num-a=10|n=II}} | {{AIME box|year=2023|num-b=8|num-a=10|n=II}} | ||
{{MAA Notice}} | {{MAA Notice}} |
Revision as of 13:10, 17 February 2023
Contents
Problem
Circles and intersect at two points and and their common tangent line closer to intersects and at points and respectively. The line parallel to that passes through intersects and for the second time at points and respectively. Suppose and Then the area of trapezoid is where and are positive integers and is not divisible by the square of any prime. Find
Solution 1
Denote by and the centers of and , respectively. Let and intersect at point . Let and intersect at point .
Because is tangent to circle , . Because , . Because and are on , is the perpendicular bisector of . Thus, .
Analogously, we can show that .
Thus, . Because , , , , is a rectangle. Hence, .
Let and meet at point . Thus, is the midpoint of . Thus, .
In , for the tangent and the secant , following from the power of a point, we have . By solving this equation, we get .
We notice that is a right trapezoid. Hence,
Therefore,
Therefore, the answer is .
~Steven Chen (Professor Chen Education Palace, www.professorchenedu.com)
Solution 2
Notice that line is the radical axis of circles and . By the radical axis theorem, we know that the tangents of any point on line to circles and are equal. Therefore, line must pass through the midpoint of , call this point M. In addition, we know that by circle properties and midpoint definition.
Then, by Power of Point,
Call the intersection point of line and be C, and the intersection point of line and be D. is a rectangle with segment drawn through it so that , , and . Dropping the altitude from to , we get that the height of the rectangle is . Therefore the area of trapezoid is
See also
2023 AIME II (Problems • Answer Key • Resources) | ||
Preceded by Problem 8 |
Followed by Problem 10 | |
1 • 2 • 3 • 4 • 5 • 6 • 7 • 8 • 9 • 10 • 11 • 12 • 13 • 14 • 15 | ||
All AIME Problems and Solutions |
The problems on this page are copyrighted by the Mathematical Association of America's American Mathematics Competitions.