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Geometry Difficulty 4.2 AIME Find the answer

Triangle ABCABC and point PP in the same plane are given. Point PP is equidistant from AA and BB, angle APBAPB is twice angle ACBACB, and AC\overline{AC} intersects BP\overline{BP} at point DD. If PB=3PB = 3 and PD=2PD= 2, then ADCD=AD\cdot CD =

Pick one

Solution

The product of two lengths with a common point brings to mind the Power of a Point Theorem.
Since PA=PBPA = PB, we can make a circle with radius PAPA that is centered on PP, and both AA and BB will be on that circle. Since APB=AB^=2ACB\angle APB = \widehat {AB} = 2 \angle ACB, we can see that point CC will also lie on the circle, since the measure of arc AB^\widehat {AB} is twice the measure of inscribed angle ACB\angle ACB, which is true for all inscribed angles.

Since PDBPDB is a line, we have PD+DB=PBPD + DB = PB, which gives 3=DB+23 = DB + 2, or DB=1DB = 1.
We now extend radius PB=3PB = 3 to diameter EB=6EB = 6. Since EDBEDB is a line, we have ED+DB=EBED + DB = EB, which gives ED+1=6ED + 1 = 6, or ED=5ED = 5.
Finally, we apply the power of a point theorem to point DD. This states that ADDC=DBDEAD \cdot DC = DB \cdot DE. Since DB=1DB = 1 and DE=5DE = 5, the desired product is 55, which is A\boxed{A}.

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Source: NuminaMath-1.5, licensed Apache-2.0. Statement and solution reproduced as published; topic and difficulty added by this site.