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Bunuel
For some values of x, the expression \(\frac{x^{(a^3)}}{x^{(ab^2)}}\) is negative. If a and b are integers, which of the following must be true?

A. a is positive
B. a is even
C. b is positive
D. b is even
E. b is odd


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\(\frac{x^{(a^3)}}{x^{(ab^2)}}\) = \(x^{(a^3-ab^2)}\)
For the expression to be negative, x must be negative and the power \({(a^3-ab^2)}\) must be odd

\({(a^3-ab^2)}\) = \(a (a^2 - b^2)\)

For \(a (a^2 - b^2)\) to be odd, both a and \( (a^2 - b^2)\) must be odd

\( a^2 \) is odd , \( b^2 \) must be even for the difference to be odd

Therefore b must be even

Option D
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Bunuel
For some values of x, the expression \(\frac{x^{(a^3)}}{x^{(ab^2)}}\) is negative. If a and b are integers, which of the following must be true?

A. a is positive
B. a is even
C. b is positive
D. b is even
E. b is odd


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\(\frac{x^{(a^3)}}{x^{(ab^2)}} = x^{a(a+b)(a-b)}\)

For some values of x, if the expression is negative, it means that x must be negative. If x were positive, it doesn't matter what the exponent is - the expression would never become negative (in the realm of real numbers).

For the expression to be negative, the exponent (which is given to be an integer) must be odd. So all a, (a+b) and (a - b) should be odd. So 'a' must be odd.
For (a+b) to be odd, since 'a' is odd, 'b' must be even.

Answer (D)
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