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Is \(x^2 < x – |y|\)?

(1) y > x

(2) x < 0

Rearrange the terms in the question so that y and x are isolated, is \(| y | < x- x^2\) ?

Statement 1:
Our goal is to assemble the inequality from the question. If \(y > x\), then \(y > x - x^2\) must be true as \(x^2\) is nonnegative. Then note if y is nonnegative, \(|y| = y\) and \(|y| > x - x^2\) is true. If y is negative, then we would have \(|y| > y > x- x^2\). Either way, \(|y| > x - x^2\) is true. Therefore the question can be answered with "no" and this is sufficient.

Statement 2:
\(x - x^2 = x * (1 - x)\). If x is negative, then \(x * (1 - x) = Negative * Positive = Negative\). Therefore |y| is always greater than \(x*(1-x) = x - x^2\). Again we answer "no" so this is sufficient.

Ans: D

How can you just "rearrange" the variables presented in the inequality equation? Aren't we not supposed to do it because we don't know the sign of these variables? I am confused :S
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Genoa2000
Is \(x^2 < x – |y|\)?

(1) y > x

(2) x < 0

Rearrange the terms in the question so that y and x are isolated, is \(| y | < x- x^2\) ?

Statement 1:
Our goal is to assemble the inequality from the question. If \(y > x\), then \(y > x - x^2\) must be true as \(x^2\) is nonnegative. Then note if y is nonnegative, \(|y| = y\) and \(|y| > x - x^2\) is true. If y is negative, then we would have \(|y| > y > x- x^2\). Either way, \(|y| > x - x^2\) is true. Therefore the question can be answered with "no" and this is sufficient.

Statement 2:
\(x - x^2 = x * (1 - x)\). If x is negative, then \(x * (1 - x) = Negative * Positive = Negative\). Therefore |y| is always greater than \(x*(1-x) = x - x^2\). Again we answer "no" so this is sufficient.

Ans: D

How can you just "rearrange" the variables presented in the inequality equation? Aren't we not supposed to do it because we don't know the sign of these variables? I am confused :S
You can't multiply and divide inequalities with variables whose signs are unknown, as that could flip the inequality. Addition and subtraction, however, can be performed as that doesn't result in any flipping of the inequality and you can just treat it as a normal equation, that is, mentally replace the < or > with =. Just remember to "mentally" put the inequality back after you're done moving things around.
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Riri1234

How can you just "rearrange" the variables presented in the inequality equation? Aren't we not supposed to do it because we don't know the sign of these variables? I am confused :S

Riri1234 thanks for the question!

For the most part, we can treat inequalities as the same as equations. We can "move" terms around using addition/subtraction, and we are allowed to perform most identical operations on both sides of the inequalities. The tricky part as you mentioned is when we involve signs, we have to be careful when doing multiplication/division with negative numbers/variables because -2 > -5 but 2 < 5. That doesn't mean we should never multiply/divide both sides by negative numbers though, given the right conditions we can still simplify.

\(x^2 < xy\) cannot be simplified unless we knew more about x, if we knew x was positive when we can cut this down to \(x < y\). If we knew x was negative then this simplifies to \(x > y\) for example.
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