Canada 2002 problem:2(Good)

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sourav das
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Canada 2002 problem:2(Good)

Unread post by sourav das » Mon Aug 01, 2011 12:13 am

Let $\tau$ be a circle with radius $r$. Let $A$ and $B$ be distinct
points on $\tau$ such that $AB < \sqrt{3}r$. Let the circle with center $B$ and
radius $AB$ meet $\tau$ again at $C$. Let $P$ be the point inside $\tau$ such that
triangle $ABP$ is equilateral. Finally, let line $CP$ meet $\tau$ again at $Q$.
Prove that $PQ = r$.
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*Mahi*
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Re: Canada 2002 problem:2(Good)

Unread post by *Mahi* » Tue Aug 30, 2011 7:59 pm

This problem can be solved easily with complex numbers.
If we let the circle to be unit circle, then letting $A=a$ and $B=1$ , point $C$ becomes $\overline{a}= \frac 1 a$
Again, point $P$ becomes $a \omega^2+ \omega $ and then it is easy enough to find the point $m$ where $CP$ intersects the circle again and $|m-p|=1$.
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