20 17 the first volume of seventh grade mathematics winter vacation life instructs homework 13 square difference formula answer the reference answer of first grade mathematics winter vacation life instructs homework. Answer: 1. Key points of knowledge:

1.a2-b2 (1) and the square difference of, difference, identity and opposites (2); negative

2. The sum of squares of A2+2ab+B2A2-2ab+B2 plus (or minus) twice the product of these two terms.

Second, lay a solid foundation:

1.( 1)25-36 x2(2)a2-4(3)x2-4 y2(4)9 a2-4 B2(5)a2 B2-64(6)m2-N2(7)x2- 1(8) 16 k2-9(9)N2-m2+3n

2. No, it's not. No, no, number three. (1) is incorrect, 1-4x2(2) is incorrect, 4a4- b4(3) is incorrect,

4.( 1)999 1 (2)489984 5.B 6。 C 7。 D

8. (1) 9991(2) 999996 (3) 3599.96, etc.

9.( 1)x4？ 8 1 (2) x4？ 1

16 (3)x2？ 2xy？ y2？ z2

10.( 1)2 16(2)5050

1 1.xn 1？ 1

Three. Ability development

9.( 1)3969 (2)996004 (3)92 16 10.(x+y)2=36，(x-y)2=28