А) х²-6х+5= х²-1х-5х+5 = х(х-1)-5(х-1) = (х-1)(х-5)
б) х²+4ху-5у² = х²+4ху+4у²-9у² = (х+2у)² - 9у² = (х+2у-3у)(х+2у+9у)
(x-1)(x-2)(x+3)-(x+1)(x+2)(x-3)=(х²-2х-х+2)(х+3)-(х²+2х+х+2)(х-3) =
= (х²-3х+2)(х+3)-(х²+3х+2)(х-3) = х³+3х²-3х²-9х+2х+6-х³+3х²-3х²+9х-2х+6 =
= 12