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If x > 0, the value of 6√x - x – 8 is greatest when x

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by hazelnut01 » Fri May 19, 2017 12:03 am
If x > 0, the value of 6√x - x – 8 is greatest when x=

A. 0.1

B. √63

C. √72

D. √81

E. √121

OA=D
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by [email protected] » Fri May 19, 2017 10:03 am
Hi ziyuenlau,

This question can be solved by TESTing THE ANSWERS. I'm going to offer a few hints so that you can retry this question on your own:

[spoiler]
1) It's worth noting that the the "-8" in the calculation can be ignored (since it would have the same 'math effect' on all 5 calculations)
2) Answers D and E can be rewritten as 9 and 11, respectively.
3) Graphing this out would form a parabola (we know this because the prompt states that there IS a 'greatest' value, so all of the others on both "sides" would be smaller). Thus, if you TEST an answer and then find the two adjacent answers lead to smaller totals, then you can stop working.
[/spoiler]

Final Answer: D

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Rich
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