Cubic formula (a-b)3 is a complete cubic difference formula. The complete cubic difference formula is a mathematical formula, namely (a-b)? =a？ -3a？ b+3ab？ -B? Cubic sum formula. (a-b)? =a？ -3a？ b+3ab？ -B? .

Note: In (a-b)? =a？ -3a？ b+3ab？ -B? In, its number is "+,-". +,-"after the first letter is arranged, and it is a homogeneous formula (3 times for each term), and its coefficients are 1, -3, +3,-1, and the result is a quartic formula.

Decomposition process of cubic formula;

The difference between two numbers multiplied by the sum of their squares and the sum of their products is equal to the cube of the difference between two numbers.

(a-b)? =a？ -3a？ b+3ab？ -B?

So a? -B? =(a-b)？ -[-3(a？ )b+3ab？ ]=(a-b)(a-b)？ +3ab(a-b)

=(a-b)(a？ -2ab+b？ +3ab)=(a-b)(a？ +ab+b？ ：

( 1)a？ +b？ =(a+b)(a？ -ab+b？ )。

(2)a n+b n =(a+b)[a(n- 1)-a(n-2)×b+...+(- 1) (r- 1 )× a(。