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| Is q > t |
| Inequalities and Odd Exponents: Watch out for negatives! |
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Emily Sledge
MGMAT STAFF
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It is because of the positive and negative possibilities.
For (1) we have p^2 in the expression. If p #0, then it is either negative or positive. However, p^2 will always be positive because it has an even exponent. We are allowed to divide by p because it is not 0, but we also know that we don't need to "flip the sign" of the inequality because p^2 is positive. For (2), we cannot just divide by p^3 because there are two cases: If p<0, then qp^3 > tp^3 becomes q < t (we flip the sign). If p>0, then qp^3 > tp^3 becomes q > t (don't flip the sign). Without knowing p's sign, we don't know which option applies. Try some numbers to see this. If p = -1, then: q(-1)^3 > t(-1)^3 -q > -t q < t One possibility: q = 2 and t = 3 works because -2>-3 and 2<3. If p = +1, then: q(1)^3 > t(1)^3 q > t One possibility: q = 3 and t = 2 works. |
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