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Is f(x) > 0?

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Bunuel
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Is f(x) > 0? [#permalink] New post   21 Jan 2015, 02:50
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Is f(x) > 0?

(1) f(x) = (x^3)^3*(x^5)
(2) x = -2

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C
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sunaimshadmani
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Re: Is f(x) > 0? [#permalink] New post   21 Jan 2015, 06:12
Statement 1 tells that f(x) = x^14, which can never be LESS THAN 0 for any x....Sufficient.
Statement 2 is insufficient because we dont know the function.
Answer should be A.
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Re: Is f(x) > 0? [#permalink] New post   21 Jan 2015, 06:45
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A.. x^even power has to be atleast 0 if x is 0 otherwise a positive int/ fraction
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Re: Is f(x) > 0? [#permalink] New post   25 Jan 2015, 03:34
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Bunuel -

is f(x) = ((x^3)^3)*(3*(x^5))

or

f(x) = (x^3)^3*(3*(x^5))
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Re: Is f(x) > 0? [#permalink] New post   25 Jan 2015, 03:39
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vedavyas9 wrote:
Bunuel -

is f(x) = ((x^3)^3)*(3*(x^5))

or

f(x) = (x^3)^3*(3*(x^5))


It's as written \((x^3){^3}*(x^5)\).
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Re: Is f(x) > 0? [#permalink] New post   25 Jan 2015, 20:44
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If x = 0 then the value of f(x) = 0 which is not < 0. For other values of x, you need to know the sign. So A is not the answer. B gives the value of x = -2 but it doesnt tell you what f(x) is, so you need both 1) and 2) to get the result. You dont need to calculate the actual value. The powers are enough to conclude that f(x) where x = -2 is less than 0.

So the answer is (C).
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Re: Is f(x) > 0? [#permalink] New post   25 Jan 2015, 21:01
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k2kataria wrote:
If x = 0 then the value of f(x) = 0 which is not < 0. For other values of x, you need to know the sign. So A is not the answer. B gives the value of x = -2 but it doesnt tell you what f(x) is, so you need both 1) and 2) to get the result. You dont need to calculate the actual value. The powers are enough to conclude that f(x) where x = -2 is less than 0.

So the answer is (C).


hi...
(x^3)^3*x^5=x^9*x^5=x^14...
so for x=0, the value is 0..
any value other than 0, ans will be >0, as the power is an even no
therefore ans is A
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Re: Is f(x) > 0? [#permalink] New post   26 Jan 2015, 04:53
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Bunuel wrote:
Is f(x) < 0?

(1) f(x) = (x^3)^3*(x^5)
(2) x = -2

Kudos for a correct solution.


The correct answer is C. Note that x^14 is not necessarily positive, it's non-negative, meaning that for x=0, x^14 = 0.
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Re: Is f(x) > 0? [#permalink] New post   26 Jan 2015, 05:47
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Bunuel wrote:
Bunuel wrote:
Is f(x) < 0?

(1) f(x) = (x^3)^3*(x^5)
(2) x = -2

Kudos for a correct solution.


The correct answer is C. Note that x^14 is not necessarily positive, it's non-negative, meaning that for x=0, x^14 = 0.



hi the statement 1 gives us the reqd ans , which is NO...
the min value is 0 in all cases which is not <0.. so A should be the ans
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Re: Is f(x) > 0? [#permalink] New post   26 Jan 2015, 05:56
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chetan2u wrote:
Bunuel wrote:
Bunuel wrote:
Is f(x) < 0?

(1) f(x) = (x^3)^3*(x^5)
(2) x = -2

Kudos for a correct solution.


The correct answer is C. Note that x^14 is not necessarily positive, it's non-negative, meaning that for x=0, x^14 = 0.



hi the statement 1 gives us the reqd ans , which is NO...
the min value is 0 in all cases which is not <0.. so A should be the ans


Sorry, there was a typo in the stem. The question reads is f(x) > 0, not f(x) < 0. Edited.
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Re: Is f(x) > 0? [#permalink]
26 Jan 2015, 05:56
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