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Geometry Difficulty 5.0 AIME Find the answer

In unit square ABCDA B C D, points E,F,GE, F, G are chosen on side BC,CD,DAB C, C D, D A respectively such that AEA E is perpendicular to EFE F and EFE F is perpendicular to FGF G. Given that GA=4041331G A=\frac{404}{1331}, find all possible values of the length of BEB E.

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

Solution

Let BE=xB E=x, then since triangles ABE,ECF,FDGA B E, E C F, F D G are all similar, we have CE=1x,CF=C E=1-x, C F= x(1x),FD=1x(1x),DG=xx2(1x),GA=1x+x2(1x)=(1x)(x2+1)x(1-x), F D=1-x(1-x), D G=x-x^{2}(1-x), G A=1-x+x^{2}(1-x)=(1-x)\left(x^{2}+1\right), therefore it remains to solve the equation (1x)(x2+1)=4041331(1-x)\left(x^{2}+1\right)=\frac{404}{1331} We first seek rational solutions x=pqx=\frac{p}{q} for relatively prime positive integers p,qp, q. Therefore we have (qp)(p2+q2)q3=4041331\frac{(q-p)\left(p^{2}+q^{2}\right)}{q^{3}}=\frac{404}{1331}. Since both qpq-p and p2+q2p^{2}+q^{2} are relatively prime to q3q^{3}, we have q3=1331q=11q^{3}=1331 \Rightarrow q=11, so (11p)(p2+121)=404=22101(11-p)\left(p^{2}+121\right)=404=2^{2} \cdot 101, and it is not difficult to see that p=9p=9 is the only integral solution. We can therefore rewrite the original equation as (x911)(x2211x+103121)=0\left(x-\frac{9}{11}\right)\left(x^{2}-\frac{2}{11} x+\frac{103}{121}\right)=0 It is not difficult to check that the quadratic factor has no zeroes, therefore BE=x=911B E=x=\frac{9}{11} is the only solution.

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