7A:
a) \(\sqrt{\dfrac{5x^3}{49y}}=\dfrac{\sqrt{5x^3}}{7\sqrt{y}}=\dfrac{\sqrt{5x^3y}}{7y}\)
b) \(7xy\sqrt{-\dfrac{3}{xy}}=7xy\cdot\dfrac{\sqrt{-3xy}}{xy}=7\sqrt{-3xy}\)
7B:
a) \(\sqrt{\dfrac{5b}{49a^3}}=\dfrac{\sqrt{5b}}{7a\sqrt{a}}=\dfrac{\sqrt{5ab}}{7a^2}\)
b) \(-\dfrac{1}{4}ab\sqrt{\dfrac{16}{ab}}=-\dfrac{1}{4}\cdot ab\cdot\dfrac{4\sqrt{ab}}{ab}=-\sqrt{ab}\)
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