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Bunuel
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romchom2001
Bunuel
Official Solution:


If \(x\) and \(y\) are consecutive integers, \(x > y\), and \(x^2 - 1 > y^2 - 4y + x - 1\), which of the following must be true?


A. \(x < 0\)
B. \(x ≠ 2\)
C. \(y > -1\)
D. \(y ≠ 1\)
E. \(x + y > 3\)


Given that \(x\) and \(y\) are consecutive integers, and \(x > y\), we can say that \(x = y + 1\). Substituting this into the given inequality, we get:

\((y + 1)^2 - 1 > y^2 - 4y + (y + 1) - 1\);

\(y^2 + 2y + 1 - 1 > y^2 - 4y + y\);

\(2y > - 3y\);

\(5y > 0\);

\(y > 0\). \(y\) can be 1, 2, 3, 4, and so on.

Since \(y = x - 1\), we can rewrite this inequality in terms of \(x\): \(x - 1 > 0\), which gives \(x > 1\). \(x\) can be 2, 3, 4, 5, and so on.

Since \(y > 0\), then \(y\) must also be greater than -1, making option C correct.

Even though we have already determined that option C is correct, let's elaborate on the other options for the sake of understanding why they are not necessarily true:

A. \(x < 0\). We found that \(x > 1\), so this option is not true. Discard.

B. \(x ≠ 2\). Since we found that \(x > 1\), this option could be true, but it's not necessarily true. Discard.

D. \(y ≠ 1\). Since we found that \(y > 0\), this option could be true, but it's not necessarily true. Discard.

E. \(x + y > 3\). Since we found that \(y > 0\) and \(x > 1\), the smallest possible value for \(x + y\) is \(1 + 2 = 3\). Therefore, this option is not necessarily true. Discard.


Answer: C
I did the same till arriving at y>0. I eliminated all options by this. In your answer when testing the options I plugged in y=0 and x=1 to test option c and the output is 0>0 which is not possible.

Remember: we already proved that y > 0, not y ≥ 0. So y = 0 is not allowed.

That means plugging in y = 0 is invalid. The inequality only holds when y > 0, so option C (y > -1) is always true since y must be greater than 0.
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I am struggling in such question. Like another person already pointed out I too eliminated because y=0 fails the equation.
I am unable to wrap my head around how y>-1 must be true if y=0 is false. Kindly help me untangle my thought process here
Here can I also say then, that y>-1000 should also be true?
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Adit_
I am struggling in such question. Like another person already pointed out I too eliminated because y=0 fails the equation.
I am unable to wrap my head around how y>-1 must be true if y=0 is false. Kindly help me untangle my thought process here

Check other similar questions from Trickiest Inequality Questions Type: Confusing Ranges (part of our Special Questions Directory).
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