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A Right Triangle Inside Another

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January 15, 2009
ratiogeometrytrigonometry

Problem Statement

In right triangle ACE \triangle ACE, we have AC \equal{} 12, CE \equal{} 16, and EA \equal{} 20. Points B B, D D, and F F are located on AC \overline{AC}, CE \overline{CE}, and EA \overline{EA}, respectively, so that AB \equal{} 3, CD \equal{} 4, and EF \equal{} 5. What is the ratio of the area of DBF \triangle DBF to that of ACE \triangle ACE? [asy] size(200);defaultpen(linewidth(.8pt)+fontsize(8pt)); dotfactor=3;
pair C = (0,0); pair E = (16,0); pair A = (0,12); pair F = waypoint(E--A,0.25); pair B = waypoint(A--C,0.25); pair D = waypoint(C--E,0.25);
dot(A);dot(B);dot(C);dot(D);dot(E);dot(F);
label("AA",A,NW);label("BB",B,W);label("CC",C,SW);label("DD",D,S);label("EE",E,SE);label("FF",F,NE);
label("33",midpoint(A--B),W); label("99",midpoint(B--C),W); label("44",midpoint(C--D),S); label("1212",midpoint(D--E),S); label("55",midpoint(E--F),NE); label("1515",midpoint(F--A),NE);
draw(A--C--E--cycle); draw(B--F--D--cycle);[/asy]<spanclass=latexbold>(A)</span> 14<spanclass=latexbold>(B)</span> 925<spanclass=latexbold>(C)</span> 38<spanclass=latexbold>(D)</span> 1125<spanclass=latexbold>(E)</span> 716 <span class='latex-bold'>(A)</span>\ \frac {1}{4}\qquad <span class='latex-bold'>(B)</span>\ \frac {9}{25}\qquad <span class='latex-bold'>(C)</span>\ \frac {3}{8}\qquad <span class='latex-bold'>(D)</span>\ \frac {11}{25}\qquad <span class='latex-bold'>(E)</span>\ \frac {7}{16}