1958 AMC 12 Problem 47

Attempt Problem 47 of the 1958 AMC 12 below, then check your answer against the professionally curated solution from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 1958 AMC 12 solutions, or check the answer key.

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47.

ABCDABCD is a rectangle (see the accompanying diagram) with PP any point on AB.\overline{AB}. PSBDPS\perp BD and PRAC.PR\perp AC. AFBDAF\perp BD and PQAF.PQ\perp AF. Then PR+PSPR+PS is equal to:

PQPQ

AEAE

PT+ATPT+AT

AFAF

EFEF

Answer: D
Concepts:rectangleparallel linessimilarity
Difficulty rating: 2070
Small Hint:

Because PQBDPQ\parallel BD and PSAF,PS\parallel AF, identify the small parallelogram near FF and SS

Big Hint:

Use the intersection T=PQACT=PQ\cap AC to compare the right triangles PTRPTR and ATQATQ

Solution:

Since AFBDAF\perp BD and PQAF,PQ\perp AF, we have PQBD.PQ\parallel BD. Also PSBD,PS\perp BD, so PSAF.PS\parallel AF. Thus quadrilateral QPSFQPSF is a rectangle, and PS=QF. PS=QF. Let T=PQAC.T=PQ\cap AC. The diagonals of a rectangle make equal angles with side AB,AB, so PAT=APT,\angle PAT=\angle APT, giving AT=PT.AT=PT. The right triangles ATQATQ and PTRPTR are similar because they share the angle at T.T. Since their hypotenuses ATAT and PTPT are equal, AQ=PR.AQ=PR. Therefore PR+PS=AQ+QF=AF. PR+PS=AQ+QF=AF.

Thus, the correct answer is D.

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Problem 47 in Other Years

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