原式=a{[c(2b-3c)]²-[b(3c+2b)]²}=a[c(2b-3c)+b(3c+2b)][c(2b-3c)-b(3c+2b)]=a(2b²+5bc-3c²)(-2b²-bc-3c²)=-a(2b-c)(b+3c)(2b²+bc+3c²)