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Equivalent expressions SAT question

Math · Advanced Math · Medium · Answer it here, explanation included.

If x is not equal to 0, which of the following expressions is equivalent to the fraction with numerator the square root of 16 x to the fourth power, y to the eighth power, end root, and denominator x cubed, end fraction ?

ExplanationShow

Choice D is correct. Taking the square root of an exponential expression halves the exponent, so the fraction with numerator the square root of, 16 x to the fourth power times y to the eighth power, end root, and denominator x cubed, end fraction, equals, the fraction with numerator 4 x squared, times y to the fourth power, and denominator x cubed, which further reduces to the fraction with numerator 4, y to the fourth power, and denominator x. This can be rewritten as 4, x to the negative 1 power, times y to the fourth power.

Choice A is incorrect and may result from neglecting the denominator of the given expression and from incorrectly calculating the square root of 16. Choice B is incorrect and may result from rewriting 1 over x as x to the first power rather than x to the negative 1 power. Choice C is incorrect and may result from taking the square root of the variables in the numerator twice instead of once.

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