1 、( 1)D

(2)B

2 、( 1)(5x + 6)(5x - 6)

(2)m(a + b - c)

(3)(8 - a)？

(4)(x - y)(2 + a)

3 、( 1)(0.7x + 0.2y)(0.7x - 0.2y)

(2)-(2ab - 1)？

(3)-3ax(a + 2x)(a - 2x)

(4)mn(m - n)？

4、( 1)? r？ - 4

(2)? (R + 2r)(R - 2r)？ 176(cm？ )

Group b

5 、( 1) 16x + 12y

(2)p？ = q

6 、( 1)(m - n)？ (m + n)

(2) 1/2ab(a + 2b)？

7 、( n + 5) - (n - 1)？ = 12(n+2), n is an integer, so it must be divisible by 12.

Group c

8 、-2ab(a + b)。 - 10

Nine times three? ( 1/3a？ + 13/3)= 4? (3/2a + 1)，

Get an a? -6a+9 = 0, a = 3 ... So the length of the wire is 22 cm.

Bian Xiao suggested: