seriy007 (а-3b)(a+3b)+4c(3b-c)

1-(2x+y)

samotugaa A^2-9b^2+12bc-4c^2=a^2-(9b^2-12bc+4c^2)=a^2-(3b-2c)^2=(a-3b+2c)×(a+3b-2c). 1-4x^2-4xy-y^2=1-(4x^2+4xy+y^2)=1-(2x+y)^2=(1-2x-y)×(1+2x+y).