Question 424566
 4 sqrt 81x^5 y^9
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= 4*sqrt[81x^4y^8*xy]
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= 4*sqrt(81x^4y^8)*sqrt(xy)
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= 4*9x^2y^4*sqrt(xy)
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= 36x^2y^4*sqrt(xy)
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Cheers,
Stan H.
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