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If a#b = a2 – a, where b ≥ 0, what is the value of (–4)#4? (

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If a#b = a2 – a, where b ≥ 0, what is the value of (–4)#4? ( [#permalink] New post 27 Jul 2018, 07:00
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Question Stats:

82% (00:29) correct 17% (00:54) wrong based on 29 sessions
If \(a\sharp b = a^2\sqrt{b} - a\), where \(b ≥ 0\), what is the value of \((–4)\sharp 4\)?

(A) –36
(B) –28
(C) 12
(D) 28
(E) 36
[Reveal] Spoiler: OA

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Re: If a#b = a2 – a, where b ≥ 0, what is the value of (–4)#4? ( [#permalink] New post 12 Aug 2018, 04:54
Expert's post
Explanation

This problem defines a function for the made-up symbol #.

In this problem a = (–4) and b = 4.

Plug the values into the function: \((-4)^2 \sqrt{4}- (-4) = 16 \times 2 + 4 = 36\).

Do not forget to keep the parentheses around the –4!

Also note that only the positive root of 4 applies, because the problem has been presented in the form of a real number underneath the square root sign.
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Re: If a#b = a2 – a, where b ≥ 0, what is the value of (–4)#4? ( [#permalink] New post 08 Jan 2020, 16:49
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Updated the question
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Re: If a#b = a2 – a, where b ≥ 0, what is the value of (–4)#4? ( [#permalink] New post 02 Nov 2020, 19:16
sandy wrote:
Explanation

This problem defines a function for the made-up symbol #.

In this problem a = (–4) and b = 4.

Plug the values into the function: \((-4)^2 \sqrt{4}- (-4) = 16 \times 2 + 4 = 36\).

Do not forget to keep the parentheses around the –4!

Also note that only the positive root of 4 applies, because the problem has been presented in the form of a real number underneath the square root sign.
----why -28 is not answer?
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Re: If a#b = a2 – a, where b ≥ 0, what is the value of (–4)#4? ( [#permalink] New post 03 Nov 2020, 11:19
Expert's post
It is just a matter of substitution

a=-4 and b=4

\(a^2 \sqrt{b} - a\)

\(-4^2 \sqrt{4} - (-4)
\)

\(16 \times 2+4=36
\)

Regards
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Re: If a#b = a2 – a, where b ≥ 0, what is the value of (–4)#4? (   [#permalink] 03 Nov 2020, 11:19
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