Question 91381
Simplify: square root of 7(5 square root5-3 square root 7) 
= [sqrt(7)][5sqrt(5) - 3sqrt(7)]

= 5sqrt(35) -3*7

= 5sqrt(35) - 21

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and also 
simplify: Square root 75a^2 over square root5 
[sqrt(75a^2]/[sqrt(5)]
=sqrt[75a^2/5]

= sqrt[15a^2]

=  a*sqrt(15)

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Cheers,
Stan H.