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If x > 0, What is the least possible value of -2√(5x) +

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by Scott@TargetTestPrep » Tue May 21, 2019 6:26 pm
BTGmoderatorDC wrote:If x > 0, What is the least possible value of -2√(5x) + x + 9 ?


A. 0
B. 1
C. √5
D. 4
E. 9

OA D

Source: e-GMAT
Notice that (√x - √5)^2 = (√x)^2 + (√5)^2 - 2(√x)(√5) = x + 5 - 2√(5x). Therefore,

-2√(5x) + x + 9 = (√x - √5)^2 + 4

Since the minimum value of (√x - √5)^2 is 0, then the minimum value of -2√(5x) + x + 9 is:

(√x - √5)^2 + 4 = 0 + 4 = 4

Answer: D

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