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Turkish NMO First Round - 1999 P-05 (Geometry)

Source:

July 3, 2012
geometry

Problem Statement

Let ABC ABC be an isosceles triangle with \left|AB\right| \equal{} \left|AC\right| \equal{} 10 and \left|BC\right| \equal{} 12. P P and R R are points on [BC] \left[BC\right] such that \left|BP\right| \equal{} \left|RC\right| \equal{} 3. S S and T T are midpoints of [AB] \left[AB\right] and [AC] \left[AC\right], respectively. If M M and N N are the foot of perpendiculars from S S and R R to PT PT, then find MN \left|MN\right|.
(A)\ \frac {9\sqrt {13} }{26} \qquad(B)\ \frac {12 \minus{} 2\sqrt {13} }{13} \qquad(C)\ \frac {5\sqrt {13} \plus{} 20}{13} \qquad(D)\ 15\sqrt {3} \qquad(E)\ \frac {10\sqrt {13} }{13}