把下列各式因式分解 (1)2x 2 -4x (2)a 2 b 2 -a 2 c 2 (3)8a 3 b 2 -12ab 3 c+6a 3 b 2 c (4)8a(x-a)+4b(a-x)-6c(x-a) (5)-x 5 y 3 +x 3 y 5 (6)(a+b) 2 -9(a-b) 2 (7)-8ax 2 +16axy-8ay 2 (8)5m(x-y) 2 +10n(y-x) 3 (9)(a 2 +1) 2 -4a 2 (10)m 2 +2n-mn-2m (11)(a 2 -4a+4)-c 2 (12)x 2 +6x-27 (13)9+6(a+b)+(a+b) 2 (14)(x+3y) 2 +(2x+6y)(3y-4x)+(4x-3y) 2 .