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# For any two numbers a and b, the operation a#b is given by the express

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Director
Joined: 08 Jun 2013
Posts: 543
Location: France
Schools: INSEAD Jan '19
GMAT 1: 200 Q1 V1
GPA: 3.82
WE: Consulting (Other)
For any two numbers a and b, the operation a#b is given by the express  [#permalink]

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04 Oct 2018, 11:07
00:00

Difficulty:

15% (low)

Question Stats:

92% (01:23) correct 8% (02:13) wrong based on 29 sessions

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For any two numbers a and b, the operation a#b is given by the expression $$a^2 + 6ab + b^2$$. If a#1 = -7, then a could be equal to

A) -3
B) -1
C) -4
D) 2
E) 4

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Director
Joined: 19 Oct 2013
Posts: 516
Location: Kuwait
GPA: 3.2
WE: Engineering (Real Estate)
Re: For any two numbers a and b, the operation a#b is given by the express  [#permalink]

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04 Oct 2018, 11:33
Harshgmat wrote:
For any two numbers a and b, the operation a#b is given by the expression $$a^2 + 6ab + b^2$$. If a#1 = -7, then a could be equal to

A) -3
B) -1
C) -4
D) 2
E) 4

$$a^2 + 6a + 1 = -7$$

$$a^2 + 6a + 8 = 0$$

$$(a+4) (a+2) = 0$$

$$a = -2$$ or $$-4$$

You could do it by backsolving and picking a number from the answer choice.

If we try a = -4

then $$(-4)^2 + 6 * -4 * 1 + 1 = 16 -24 + 1 = -7$$
Re: For any two numbers a and b, the operation a#b is given by the express   [#permalink] 04 Oct 2018, 11:33
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# For any two numbers a and b, the operation a#b is given by the express

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