Question 187424
2r^-5 y^3 over n^2 divided by r^2 y^5 over 2n 

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[(2y^3/r^5)/n^2] / [r^2y^5/2n]

= [(2n^2y^3/r^5] * [2n/r^2y^5]

Cancel factors that are common to any numerator and a denominator,
such as y^3

= [(2n^2/r^5] * [2n/r^2y^2]

= [4n^3] / [r^7y^2]

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Cheers,
Stan H.