Its variant is often used in solving problems: (a+b)3 = a3+B3+3ab(a+b)a3+B3 =? (a+b)3- 3ab(a+b).

Don't underestimate this deformation. If you are very familiar with this deformation, it is very useful in simplification and evaluation, which is helpful to solve the problem.

For example: [(x-y) × (√ x+√ y)+3 (x √ y-y √ x+y) = [(√ x-√ y)+3 √ xy × (√ x-√ y)]/(x

Formula decomposition:

Decomposition steps: (a+b) 3 = (a+b) (a+b) (a+b) = (a2+2ab+B2) (a+b) = a3+3a2b+3ab2+B3.

Promotion:

(x 1+x2+x3+...+xn)(x 1+x2+x3……+xn)2

=(x 1+x2+x3……+xn)(x 12+x22+x32……+xn2+2x 1x 2+2x 1x 3+......+2x(n- 1)xn)

= x 13+x23+x33+……+xn3+3x 12 x2+3x 22 x 1+……+3[x(n- 1)]2xn