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If a<b<0 which of the following numbers must be positive?

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If a<b<0 which of the following numbers must be positive? [#permalink] New post 30 Jan 2016, 09:21
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Question Stats:

65% (00:45) correct 34% (00:40) wrong based on 29 sessions
If \(a<b<0\) which of the following numbers must be positive?

Indicate all such numbers.

A) \(a - b\)
B) \(a^2 - b^2\)
C) \(ab\)
D) \(a^2b\)
E) \(a^2b + ab^2\)

[Reveal] Spoiler:
B and C


Practice Questions
Question: 15
Page: 469
Difficulty: medium


B and C
[Reveal] Spoiler: OA

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Re: If a<b<0 which of the following numbers must be positive? [#permalink] New post 30 Jan 2016, 09:25
Expert's post
Solution

The values a = -3 and b = -2 satisfy the given inequality.

So, let's plug these values for a and b into the answer choices....

A) (-3) - (-2) = -1 NEGATIVE

B) (-3)² - (-2)² = 9 - 4 = 5 POSITIVE

C) (-3)(-2) = 6 POSITIVE

D) (-3)²(-2) = -18 NEGATIVE

E) (-3)²(-2) + (-3)(-2)² = (-18) + (-12) = -30 NEGATIVE

Substitute and you come up with the answers B and C
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Re: If a<b<0 which of the following numbers must be positive? [#permalink] New post 04 Sep 2018, 20:01
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B and C will be the answer
a^2 - b^2 will positive because a<b and both are negative numbers. Squaring them will make them positive and a will be bigger than b.
C is a answer cause negative * negative = positive.
Re: If a<b<0 which of the following numbers must be positive?   [#permalink] 04 Sep 2018, 20:01
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If a<b<0 which of the following numbers must be positive?

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