69. b² +4 - b = b²+4 - b = b²+4 - b(b-2) =
b² -4 b+2 (b-2)(b+2) b+2 (b-2)(b+2)
= b² +4 -b² +2b = 4+2b = 2(b+2) = 2
(b-2)(b+2) (b-2)(b+2) (b-2)(b+2) b-2
70. a²+9 - a = a² +9 - a = a² +9 - a(a-3) =
a² -9 a+3 (a-3)(a+3) a+3 (a-3)(a+3)
= a² +9 -a² +3a = 9+3a = 3(a+3) = 3
(a-3)(a+3) (a-3)(a+3) (a-3)(a+3) a-3
71. 2a - 1 = 2a - 1 = 2a - (a-3) = 2a -a +3 =
a² -9 a+3 (a-3)(a+3) a+3 (a-3)(a+3) (a-3)(a+3)
= a+3 = 1
(a-3)(a+3) a-3