2011 AMC 10A Problem 7

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Concepts:absolute valueradical

Difficulty rating: 960

7.

Which of the following equations does not have a solution?

(x+7)2=0(x + 7)^2 = 0

3x+5=0|-3x| + 5 = 0

x2=0\sqrt{-x} - 2 = 0

x8=0\sqrt{x} - 8 = 0

3x4=0|-3x| - 4 = 0

Solution:

A simplifies to x+7=0 x + 7 = 0 x=7, x = -7, so it has a solution.

B simplifies to 3x=5, |-3x| = -5, which has no solution since absolute value makes everything positive.

Let us make sure that all the other choices have solutions.

C simplifies to x=2 \sqrt{-x} = 2 x=4 -x = 4 x=4, x = -4, which is fine.

D simplifies to x=8 \sqrt{x} = 8 x=64, x = 64, which works.

Finally, E simplifies to 3x=4 |-3x| = 4 3x=±4 -3x = \pm 4 x=±43, x = \pm \dfrac{4}{3}, which has a solution as well.

Thus, B is the correct answer.

Problem 7 in Other Years