1. If there is a common factor, it is necessary to extract the common factor, such as the first a? -a, whose common factor is a, puts forward a, that is, =a*(a? -1), and then expand with the square difference formula, =a*(a- 1)*(a+ 1).

2. For complex formulas, decompose them first, such as -y? +(y-2)？ Expand =-y？ +y？ +4-4y=4-4y=4*( 1-y), (using the complete square formula)

3. learning formula: (a+b)? (a-b)? ={(a+b)*(a-b)}？ =(a？ -B? )?

4. Use square difference formula 9(x- 1)? - 1 =[3(x- 1)]？ - 1 = { 3(x- 1)- 1 } { 3(x- 1)+ 1 } =(3x-4)*(3x-2)

5、x^4-y^4=(x？ )? -(y？ )? =(x？ -Really? )*(x？ +y？ )=(x-y)(x+y)(x？ +y？ )

6、4(x+y)？ -9(x-y)？ =[2(x+y)]？ -[3(x-y)]？ = [2 (x+y)+3 (x-y)] * [2 (x+y)-3 (x-y)] = (5x-y) (5y-x) (Note that a plus sign may be written as a minus sign, right? In short, solve it with square difference. )