а) 9m^2-9mn-5m+5n= 9m(m-n) -5(m-n)= (m-n) (9m-5)
б) bc+3ac-2ab-6a^2= b(c-2a) +3a(c-2a)= (c-2a) (b+3a)
в) z^3+21+3z+7z^2= z^2(z+7)+3(z+7)= (z+7) (z^2+3)
г) z-3z^2+z^3-3= (z-3)+z^2(z-3)= (z-3) (1+z^2)
