Question

How can sums and differences of cubes be identified for factoring?

Answer 1

The sum of cubes is given as:
a³ + b³ = (a + b)(a² - ab + b²)

Example for the sum of cubes:

64x³+y³ ⇒ This is the sum of cubes because each term; 64, x³, and y³ are cube numbers

By writing each term as an expression of cube numbers, we have:
(4x)³ + (y)³ ⇒ 64 is 4³
Use the factorization of the sum of cubes, we have:
(4x + y) ( (4x)²- 4xy + y²)
(4x + y) (16x² - 4xy + y²)

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The difference of cubes can be factorized as:
(x³ - y³) = (x - y)(x² + xy + y²)

Example
(125x³ - 8y³) = (5x - 2y) ((5x)² + (5x)(2y) + (2y)²)
                     = (5x - 2y) (25x² + 10xy + 4y²)