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Question
Simplify using following identity : `( a +- b )(a^2 +- ab + b^2) = a^3 +- b^3`
`( 3x - 5/x )( 9x^2 + 15 + 25/x^2)`
Solution
`( 3x - 5/x )( 9x^2 + 15 + 25/x^2)`
=`( 3x - 5/x )[ (3x)^2 + (3x)(5/x) + (5/x)^2 ]`
= `(3x)^3 - (5/x)^3`
= `27x^3 - 125/x^3`
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