2022 AMC 10B Problem 22
Below is the professionally curated solution for Problem 22 of the 2022 AMC 10B, from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 2022 AMC 10B solutions, or check the answer key.
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Difficulty rating: 2390
22.
Let be the set of circles in the coordinate plane that are tangent to each of the three circles with equations What is the sum of the areas of all circles in
Solution:
Let be circle be circle and be circle
First note that every circle, in is internally tangent to Then we case on the tangency of with and
Case This corresponds to the pink circle. This is where and are internally tangent to
Case This corresponds to the bluish circle. This is where and are externally tangent to
Case This corresponds to the green circle. This is where is externally and is internally tangent to
Case This corresponds to the red circle. This is where is internally and is externally tangent to
We can consider cases and together. Note that and have the same center. This means that the line connecting the center of and passes through the tangency point of both and and and
This line is the diameter of and it has length Therefore, the radius of is
Consider cases and together. Similarly to above, the line connecting the center of and will pass through the tangency points.
This time, however, the diameter of is This makes the radius of
contains circles: of which have radius and of which have radius (this is because we can flip all the circles in the diagram over the x-axis to get more circles).
The total area of the circles in is therefore Thus, E is the correct answer.
Problem 22 in Other Years
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