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That was rather a quick reply, thanx. I'll post the OA as and when i get some more replies. However, I have just a couple of questions

1) Why do we not sovle this problem by simply backsolving and determining the option which returns the least value using the equation? Why are you finding out the range?

2) In your solution, why have u changed the inequality sign in "z<-3/2" ?
ie. shouldng it be z>-3/2 or z>1/2 ?...but even then this range doesnt make sense.

3) One question regarding how to use this forum more effectively: how do i set an email alert when i wish to track all the replies that are posted to this question. There is an option "Notify me when a reply is posted". But i am notified when i get only one reply!

Re: PS - Value of z [#permalink]
19 Oct 2005, 09:50

cdaat wrote:

What is the minimum value of z for which (z^2)+z-(3/4)>0 is not true?

(A) -5/2 (B) -3/2 (C) -1/2 (D) 1/4 (E) 1/2

z^+z-3/4=(z+1/2)^2-1
It>0 is not true means it has to be less or equal to 0.
(z+1/2)^2-1<=0
(z+1/2)^2<=1
-1<=z+1/2<=1
-3/2<=z<=1/2
The minimum value of z is thus -3/2. _________________

Keep on asking, and it will be given you;
keep on seeking, and you will find;
keep on knocking, and it will be opened to you.

Last edited by HongHu on 19 Oct 2005, 09:58, edited 1 time in total.

I went about solving the problem a little different.

Because the question asked for the least values I decided to plug in the second least value and solve. I would have adjusted my next value based on the answer i received. Because i got =0. I didnt' go any further.

It isn't very technical but it made it quick to solve.

I went about solving the problem a little different.

Because the question asked for the least values I decided to plug in the second least value and solve. I would have adjusted my next value based on the answer i received. Because i got =0. I didnt' go any further.

It isn't very technical but it made it quick to solve.

agree, this one is ok and not too complicated, you can definitely plug and play

Yes. I often make such errors, oops. Let it be an example for you not to do it in the real test.

Unfortunately Mr. Honghu such errors are the bane of my existence.

hmmm.... Are you sure Honghu is Mr.?

It's 'Ms.' !

Oops! My bad. A thousand apologies Ms. Honghu. Apparently, my data sufficiency skills for real life situations has not kept pace with the gmat.

Heh maybe I'm just a Mr HongHu pretending to be a Ms HongHu so that my mistakes are more easily tolerated ... Isn't real life more interesting and complicated. _________________

Keep on asking, and it will be given you;
keep on seeking, and you will find;
keep on knocking, and it will be opened to you.

Re: What is the minimum value of z for which z^2+z-3/4>0 [#permalink]
29 Oct 2011, 01:03

On solving the equation we get (2z+3)(2z-1)>0. The critical points for the above equation will be -3/2 and 1/2 (where value of z=0).

Now let us find put 3 no's in the equation- 2 which lie on either side of the critical points and 1 in between.

Lets say -2,0 and 2. *On filling -2 in the equation we get 5/4 which is +ve.(no number within this range (-infinity to -3/4) will satisfy the condition as they all will be more than 0)

*On filling 0 in the equation we get -3/4 which is -ve

*On filling 2 we get 21/4 which is +ve.(no number within this range (1/2 to +infinity) will satisfy the condition as they all will be more than 0)

We can safely eliminate a and c options.

Now at -3/2 and 1/2 we know value is 0. Let us check at 1/4. Value at 1/4 = -9/16 = -0.56.

Question clearly says minimum value of z where equation>0 is not true. so it means value can be 0 or less than 0. We need to find the minimum value of z and not of the equation where the condition holds. out of -3/2,1/4 and 1/2 minimum value where the condition will not be true is -3/2. Hence option b.

Hope it helps...

gmatclubot

Re: What is the minimum value of z for which z^2+z-3/4>0
[#permalink]
29 Oct 2011, 01:03