1950 AMC 12 Problem 49
Attempt Problem 49 of the 1950 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 1950 AMC 12 solutions, or check the answer key.
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49.
A triangle has a fixed base that is inches long. The median from to side is inches long and can have any position emanating from The locus of the vertex of the triangle is:
A straight line inches from
A circle with as center and radius inches
A circle with as center and radius inches
A circle with radius inches and center inches from along
An ellipse with as focus
Answer: D
Small Hint:
Let be the midpoint of ; then moves on a circle centered at
Big Hint:
In vector form, the midpoint relation gives when is the origin
Solution:
Put at the origin and regard and the midpoint of as vectors. Since the point moves on a circle of radius centered at The midpoint relation gives Thus the locus of is the image of that circle under a dilation by followed by translation by It is a circle of radius centered at
Because the point is inches from along the ray Hence the correct answer is D.