Hello Alexpavlos,
You are right in assuming that since y=-1 and x^2=y^2, x=+/-1. However, remember that equation in statement 1 also gives you a relationship between statement x and y. The correct answer should satisfy all the data. Now the question you should ask yourself is whether it is possible to use the information in statement 2 and 1 together to get a single value for x.
Statement 1 mentions that
x=2y+1
Substituting y=-1 in the this equation, we get
x=-1 and hence, x<0. Hence, together the two statements suffice.
Answer-C
Hope this helps! Let me know if you need any further clarification.
alexpavlos wrote:
Bunuel wrote:
If x^2 = y^2, is true that x>0?
\(x^2 = y^2\) --> \(|x|=|y|\) --> either \(y=x\) or \(y=-x\).
(1) x=2y+1 --> if \(y=x\) then we would have: \(x=2x+1\) --> \(x=-1<0\) (notice that in this case \(y=x=-1\)) but if \(y=-x\) then we would have: \(x=-2x+1\) --> \(x=\frac{1}{3}>0\) (notice that in this case \(y=-x=-\frac{1}{3}\)). Not sufficient.
(2) y<= -1. Clearly insufficient.
(1)+(2) Since from (2) \(y\leq{-1}\) then from (1) \(y=x=-1\), so the answer to the question is NO. Sufficient.
Answer: C.
Hope it's clear.
Hi!
I did a bit of a unnecessarily long way but got to the wrong answer and was hoping someone could tell me what my logical error is.
i squared both sides of statement 1 and got to \(x^2 = 4y^2 + 4y +1\)
then I replaced \(x^2\) with \(y^2\) and got the same as everyone else that y = -1 or y = -(1/3) NOT sufficient
Using statement B i eliminated y=-(1/3) but where I got it wrong is that I thought that since y = -1 then x could be equal to +/- 1 so I chose E
Am i missing something?
Thank you in advance or any responses!