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is a + b^4 positive?

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is a + b^4 positive?  [#permalink]

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New post 17 Aug 2018, 21:15
3
3
00:00
A
B
C
D
E

Difficulty:

  75% (hard)

Question Stats:

42% (01:20) correct 58% (01:21) wrong based on 53 sessions

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is \(a + b^{4}\) positive?
a) b > a
b) \(b^{2} > a^{2}\)

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Re: is a + b^4 positive?  [#permalink]

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New post 17 Aug 2018, 21:39
2
GMATbuster92 wrote:
is \(a + b^{4}\) positive?
a) b > a
b) \(b^{2} > a^{2}\)


I) \(b = 3, a =2\).. \(a + b^{4}\) is positive.
\(b = 2, a= -20\)... \(a+b^{4}\) is negative.

II) \(b = 3, a = 2\)... \(a + b^{4}\) is positive.
b = \(1/\sqrt{2}\), a = \(-1/\sqrt{3}\).... \(a + b^{4}\) is negative.

Hence, \(E\).
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is a + b^4 positive?  [#permalink]

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New post 17 Aug 2018, 22:00
GMATbuster92 wrote:
is \(a + b^{4}\) positive?
a) b > a
b) \(b^{2} > a^{2}\)


First don't try to pick the numbers for this, Just see if you can find 2 things with the given statements

1. Is a -ve or +ve
2. Is a>b

if you cannot answer any one of the above, the answer comes - it's E
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Re: is a + b^4 positive?  [#permalink]

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New post 17 Aug 2018, 22:09
is \(a + b^{4}\) positive?
a) b > a
a=1 and b=2.....yes
a=-1/3 and b = 0.....no
insuff

b) \(b^{2} > a^{2}\)
a=2, b=4.....yes
a=-1/3 and b = 1/2 ....No
insuff

combined
a=2, b=4.....yes
a=-1/3 and b = 1/2 ....No
insuff

E
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Re: is a + b^4 positive?  [#permalink]

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New post 17 Aug 2018, 23:00
Hi everyone..

Can we not solve without using numbers?

I took square root b =|b|

But wasn't able to figure out what to do nect

Posted from my mobile device
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Re: is a + b^4 positive?  [#permalink]

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New post 17 Aug 2018, 23:16
chetan2u wrote:
is \(a + b^{4}\) positive?
a) b > a
a=1 and b=2.....yes
a=-1/3 and b = 0.....no
insuff

b) \(b^{2} > a^{2}\)
a=2, b=4.....yes
a=-1/3 and b = 1/2 ....No
insuff

combined
a=2, b=4.....yes
a=-1/3 and b = 1/2 ....No
insuff

E



chetan2u, can we do this without assuming numbers? like algebraically or the number line please?
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Re: is a + b^4 positive? &nbs [#permalink] 17 Aug 2018, 23:16
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