1955 AMC 12 Problem 28

Attempt Problem 28 of the 1955 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 1955 AMC 12 solutions, or check the answer key.

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28.

On the same set of axes are drawn the graph of y=ax2+bx+cy=ax^2+bx+c and the graph of the equation obtained by replacing xx by x-x in the given equation. If b0b\ne0 and c0c\ne0 these two graphs intersect:

in two points, one on the xx-axis and one on the yy-axis

in one point located on neither axis

only at the origin

in one point on the xx-axis

in one point on the yy-axis

Answer: E
Concepts:parabola reflectionsimultaneous equationssymmetry
Difficulty rating: 1340
Small Hint:

The reflected graph is y=ax2bx+cy=ax^2-bx+c

Big Hint:

Set the two expressions for yy equal and use b0b\ne0

Solution:

Replacing xx by x-x gives y=ax2bx+c.y=ax^2-bx+c. At an intersection, ax2+bx+c=ax2bx+c, ax^2+bx+c=ax^2-bx+c, so 2bx=0.2bx=0. Since b0,b\ne0, we must have x=0,x=0, and then y=c0.y=c\ne0. There is exactly one intersection, (0,c),(0,c), on the yy-axis.

Thus, the correct answer is E.

← Problem 27#27
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