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Which of the following must be non-negative?

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by GMATGuruNY » Sat Jan 05, 2019 5:42 am
BTGmoderatorDC wrote:Which of the following must be non-negative?

A. (a-0.9)(a-1)

B. (a+1)(a-1)

C. (a+0.9)(a+1)

D. (a-0.9)(a-0.9)

E. a(a+1)
D: (a-0.9)(a-0.9) = (a-0.9)².
The square of a value cannot be negative.

The correct answer is D.
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by Scott@TargetTestPrep » Fri Feb 01, 2019 5:40 pm
BTGmoderatorDC wrote:Which of the following must be non-negative?

A. (a-0.9)(a-1)

B. (a+1)(a-1)

C. (a+0.9)(a+1)

D. (a-0.9)(a-0.9)

E. a(a+1)

OA D

Source: Economist GMAT
Since a perfect square is always non-negative, we see that (a - 0.9)(a - 0.9) = (a - 0.9)^2 is always non-negative.

Answer: D

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