can someone explain to me how they got in the numerator?

problem:

first step:

I know they used the perfect cube formula, but why use 16 and 4. and where did the come from?

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- November 28th 2009, 10:27 AMvd853Perfect cube decomposition question
can someone explain to me how they got in the numerator?

problem:

first step:

I know they used the perfect cube formula, but why use 16 and 4. and where did the come from? - November 28th 2009, 10:54 AMmasters
- November 28th 2009, 01:55 PMvd853
Thanks! did not know about the difference formula.