Please post in DS section.
Here we need to know the sign of x^n, to figure out whether the expression would be negative or not.
Should be C
if n is an integer, is -3x^n positive?
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Source: Beat The GMAT — Data Sufficiency |
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this_time_i_will
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selango
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-3x^n +ve?
stmt1,
x is -ve.
n is even.-3x^n is negative
n is odd.-3x^n is positive.
Insuff
stmt2,
n is odd.
x is positive.-3x^n is negative
x is negative.-3x^n is positive.
Insuff
Combining 1 and 2,
x is -ve and n is odd
x^n is negative.
(-3)*negative=positive
Suff
Pick C
stmt1,
x is -ve.
n is even.-3x^n is negative
n is odd.-3x^n is positive.
Insuff
stmt2,
n is odd.
x is positive.-3x^n is negative
x is negative.-3x^n is positive.
Insuff
Combining 1 and 2,
x is -ve and n is odd
x^n is negative.
(-3)*negative=positive
Suff
Pick C
--Anand--
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kvcpk
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if n is an integer, is -3x^n positive?
1. x is negative.
Let x = -1, n = 0
-3x^n = -3.. Negative
Let x = -1, n = 1
-3x^n = 9 .. Positive
INSUFF
2. n is odd.
Let n = 1, x = 1
-3x^n = -3.. Negative
Let n=1, x=-1
-3x^n=3.. Positive
INSUFF
Combining:
x<0
When x is less than 0, all odd powers of x are negative.
hence x^n <0
-3(negative) = always positive
HENCE SUFF
pick C
1. x is negative.
Let x = -1, n = 0
-3x^n = -3.. Negative
Let x = -1, n = 1
-3x^n = 9 .. Positive
INSUFF
2. n is odd.
Let n = 1, x = 1
-3x^n = -3.. Negative
Let n=1, x=-1
-3x^n=3.. Positive
INSUFF
Combining:
x<0
When x is less than 0, all odd powers of x are negative.
hence x^n <0
-3(negative) = always positive
HENCE SUFF
pick C
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outreach
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if n is an integer, is -3x^n positive?
1. x is negative.
2. n is odd.
1. x is negative.
n=1,then -3x^n will be positive
n=2,then -3x^n will be -ve
insuff
2. n is odd.
no idea abt sign of n
x can be +ve or -ve
insuff
combined
suff
C
1. x is negative.
2. n is odd.
1. x is negative.
n=1,then -3x^n will be positive
n=2,then -3x^n will be -ve
insuff
2. n is odd.
no idea abt sign of n
x can be +ve or -ve
insuff
combined
suff
C
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