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Geometry Difficulty 5.3 AIME, harder Find the answer

G3.3 ABCDA B C D is a cyclic quadrilateral. ACA C and BDB D intersect at GG. Suppose AC=16 cm,BC=CD=8 cmA C=16 \mathrm{~cm}, B C=C D=8 \mathrm{~cm}, BG=x cmB G=x \mathrm{~cm} and GD=y cmG D=y \mathrm{~cm}. If xx and yy are integers and x+y=cx+y=c, find the value of cc.

A number or a short expression. Spacing and $ signs are ignored.

Solution

As shown in the figure, let CG=t,AG=16tC G=t, A G=16-t.
Let CBG=θ,ACB=α\angle C B G=\theta, \angle A C B=\alpha.
Then CAB=θ\angle C A B=\theta (eq. chords eq. \angle s)
Then BCGACB\triangle B C G \sim \triangle A C B (equiangular)
t:8=8:16t: 8=8: 16 (ratio of sides, Δs\sim \Delta \mathrm{s} )
t=4t=4
It is easy to see that ADGBCG\triangle A D G \sim \triangle B C G (equiangular)
(16t):y=x:t (ratio of sides, Δs ) (164)×4=xyxy=48 \begin{array}{l} (16-t): y=x: t \text { (ratio of sides, } \sim \Delta \mathrm{s} \text { ) } \\ (16-4) \times 4=x y \\ x y=48 \end{array}

Assume that xx and yy are integers, then possible pairs of (x,y)(x, y) are (1,48),(2,24),.,(6,8),,(48,1)(1,48),(2,24), \ldots .,(6,8), \ldots,(48,1).
Using triangle inequality x+t>8x+t>8 and 8+t>x8+t>x in BCG\triangle B C G, the only possible combinations are:
(x,y)=(6,8) or (8,6)c=x+y=14 \begin{array}{l} (x, y)=(6,8) \text { or }(8,6) \\ c=x+y=14 \end{array}

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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.