MathDB
Simple cevian-related problem

Source: Canadian Mathematical Olympiad - 1986 - Problem 1.

July 3, 2011
geometrytrigonometrygeometry proposed

Problem Statement

In the diagram line segments ABAB and CDCD are of length 1 while angles ABCABC and CBDCBD are 9090^\circ and 3030^\circ respectively. Find ACAC.
[asy] import geometry; import graph;
unitsize(1.5 cm);
pair A, B, C, D;
B = (0,0); D = (3,0); A = 2*dir(120); C = extension(B,dir(30),A,D);
draw(A--B--D--cycle); draw(B--C); draw(arc(B,0.5,0,30));
label("AA", A, NW); label("BB", B, SW); label("CC", C, NE); label("DD", D, SE); label("3030^\circ", (0.8,0.2)); label("9090^\circ", (0.1,0.5));
perpendicular(B,NE,C-B); [/asy]