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143) Which one is less than 0?

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by selango » Thu May 13, 2010 8:17 am
Ans II only

I option --> x3-y3(since x>y>0 the answer ll be surely >0)

II option -->x2y-x3


-->x2y-x3 = x2(y-x) (since x>y ,y-x return -ve value)

Hence less than zero

III option -->x2y-xy2= xy(x-y) It ll retrun value >0( same concept as option I)
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by M811 » Thu May 13, 2010 8:31 am
ern5231 wrote:x>y>0. Then which of the following is less than 0?
â… x3-y3
â…¡x2y-x3
â…¢x2y-xy2

â… only ,â…¡ only ,â…¢ only ,â… and â…¢ ,â…¡and â…¢

Case 1

x = 5 and y = 2

I 125 - 8 > 0
II 50 - 125 <0
III 50 - 20 >0

Case 2

X = 0.2 y =01

I 0.8 - 0.1 >0
II 0.4 - 0.8 < 0
III 0.4 - 0.2 >0

[spoiler]Ans = only II[/spoiler]
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by debmalya_dutta » Thu May 13, 2010 11:59 am
Answer is II
x2(y-x) ...since y< x ; y-x is negative and x2 is always positive. hence the product is always negative
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