2015 AMC 12B Problems/Problem 25
Problem
A bee starts flying from point . She flies inch due east to point . For , once the bee reaches point , she turns counterclockwise and then flies inches straight to point . When the bee reaches she is exactly inches away from , where , , and are positive integers and and are not divisible by the square of any prime. What is ?
Solution
Let (a angle). We're going to toss this onto the complex plane. Notice that on the complex plane is:
Therefore, we just want to find the magnitude of on the complex plane. This is an arithmetic/geometric series.
We want to find . First of all, note that because . So then:
So therefore . Let us now find :
We dropped the term because . Now we just have to find . This can just be computed directly:
Therefore
Thus the answer is
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See Also
2015 AMC 12B (Problems • Answer Key • Resources) | |
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