2006 AMC 10A Problem 8

Attempt Problem 8 of the 2006 AMC 10A 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 2006 AMC 10A solutions, or check the answer key.

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8.

A parabola with equation y=x2+bx+cy = x^2 + bx + c passes through the points (2,3)(2, 3) and (4,3).(4, 3). What is c?c?

22

55

77

1010

1111

Answer: E
Concepts:parabolasystem of equations
Difficulty rating: 1270
Solution:

Substituting the points gives 3=4+2b+c3 = 4 + 2b + c and 3=16+4b+c.3 = 16 + 4b + c. Subtracting yields 0=12+2b,0 = 12 + 2b, so b=6.b = -6.

Then c=342(6)=11.c = 3 - 4 - 2(-6) = 11.

Thus, the correct answer is E.

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