1997 AMC 12 Problem 26

Attempt Problem 26 of the 1997 AMC 12 below, then check your answer against the professionally curated solution from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 1997 AMC 12 solutions, or check the answer key.

All problems are used with official legal permission of the Mathematical Association of America (MAA).

26.

Triangle ABCABC and point PP in the same plane are given. Point PP is equidistant from AA and B,B, angle APBAPB is twice angle ACB,ACB, and AC‾\overline{AC} intersects BP‾\overline{BP} at point D.D. If PB=3PB=3 and PD=2,PD=2, then AD⋅CD=AD\cdot CD=
55
66
77
88
99
Answer: A
Concepts:circlespower of a point
Small hint:
Draw the circle centered at PP through AA and BB
Big hint:
The central-angle condition puts CC on that circle, so apply intersecting chords at DD
Solution:
Because PA=PB,PA=PB, draw their circle with center P.P. The condition ∠APB=2∠ACB\angle APB=2\angle ACB is the central-inscribed angle relation, so CC lies on the same circle. Along line PB,PB, the other circle intersection is EE with PE=3.PE=3. Power of DD gives AD⋅CD=DE⋅DB=(3−2)(3+2)=5. \begin{aligned} AD\cdot CD&=DE\cdot DB\\ &=(3-2)(3+2)=5. \end{aligned} Thus A is correct.
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