nuthan Posted May 28, 2005 Share Posted May 28, 2005 Z>0 ? 1). X*y*z>0 2). X*y*z^2>0 C Quote Link to comment Share on other sites More sharing options...
adcambridge Posted May 28, 2005 Share Posted May 28, 2005 if both (x*y) and z are pasitive or both -ve will satisfy 1 and so can not tell whethr z>0 From 2, can tell x*y is +ve but can not tell whtehr z>0 or not combining 1 and 2 we can tell whether z>0 or not Quote Link to comment Share on other sites More sharing options...
rd_eastbay Posted May 29, 2005 Share Posted May 29, 2005 (1) Insuff. (2) Insuff as z^2 is always +ve. From (2) x*y > 0. Therefore from (1) z > 0. C. Quote Link to comment Share on other sites More sharing options...
jax510 Posted June 11, 2005 Share Posted June 11, 2005 From (1) we either have three pos numbers or 2 neg and one pos number From (2) we have the same idea. Together we see that x and y are either both pos or both neg. if z were neg then x or y would also be neg making the expression neg overall. Therefore, C is correct. Quote Link to comment Share on other sites More sharing options...
SOJO Posted June 12, 2005 Share Posted June 12, 2005 stmt1) Insuff. stmt2)Insuff. Combining 1) and 2) Method1) stmt 2 can be written as (X*y*z)* z >0 which means both (x*y*z) and z are either positive or negative . stmt 1) says that (x*y*z) is positive , therefore Z is also positive. Method 2) On other note , when I tried to solve equation 1 and 2 by adding them , I am not getting correct answer . can any one tell me what’s wrong with this method? Adding stmt 1 and stmt 2. xyz+xyz^2>0 => xyz(1+z)>0 => both xyz and (1+z) are either +ive or -ive. since stmt1 tells us xyz is +ive => 1+z is also +ive => 1+z>0 => z>-1 but in this solution value of Z could be 0 or greater then zero . Quote Link to comment Share on other sites More sharing options...
Synergy79 Posted July 7, 2005 Share Posted July 7, 2005 Soln for xyz(1+z) > 0 results in Z > -1. But you assumed xyz > 0. Say if z=-0.5 then xy Hence z 0. Hence Z > 0 is the only possible soln. Ans ( C ) Quote Link to comment Share on other sites More sharing options...
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