2019 AIME #13 (problem request)
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Triangle $ABC$ has side lengths $AB=4$, $BC=5$, and $CA=6$. Points $D$ and $E$ are on ray $AB$ with $AB<AD<AE$. The point $F \neq C$ is a point of intersection of the circumcircles of $\triangle ACD$ and $\triangle EBC$ satisfying $DF=2$ and $EF=7$. Then $BE$ can be expressed as $\tfrac{a+b\sqrt{c}}{d}$, where $a$, $b$, $c$, and $d$ are positive integers such that $a$ and $d$ are relatively prime, and $c$ is not divisible by the square of any prime. Find $a+b+c+d$.
Let $P=AE\cap CF$, $CP=5x$, and $BP=5y$. By $\triangle{CBP}\sim\triangle{EFP}$, we know that $EP=7x$ and $FP=7y$. By $\triangle{CAP}\sim\triangle{DFP}$ we know that $$\frac{6}{4+5y}=\frac{2}{7y} \implies y=\frac{1}{4}.$$ Hence $BP=\frac{5}{4}$ and $FP=\frac{7}{4}$. Note that the similar triangles also give $DP=\frac{5}{3}x$ so $DE=\frac{16}{3}x$. Then, by Stewart's Theorem on $\triangle{FEP}$ and cevian $FD$, we obtain \[\frac{560}{9}x^3+28x=\frac{49}{3}x+\frac{245}{3}x \implies x=\frac{3\sqrt{2}}{4}.\] Finally, we get $BE=\frac{5}{4}+7x=\frac{5+21\sqrt{2}}{4}$ so the answer is $\boxed{032}$ as desired.
hi
ReplyDeletei requested this problem
solution looks short
but its actually rlly rlly hard to come up with it
but thanks for the sol
this is a multi-purpose math olympiad site
better than aops i'd say im ngl
being honest here
their name is just "art of problem solving"
but what you are doing is the REAL art
what they do is just a basic level of what ur doing
ur doing way way wayyyyy deeper
even tho you dont clearly say it
your sols immediately make me understand
how to come up with it
thanks man