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: