а)4х^2+8x=4х(х+2)
б)3m-6n+mn-2n^2 = 3(m-2n)+n(m-2n) = (m-2n)(3+n)
в)9a^2-16=3^2*a^2-4^2 = (3a)^2 - 4^2 = (3a-4)(3a+4)
г)y^3+18y^2+81y = y(y^2 + 18y + 81) = y(y+9)^2
д)x^6+27 = (x^2 + 3x) (x^4 - 3x^2 + 9) = (x^2 + 3) (x^4 -3x^3 + 3x^3 + 3x^2 - 9x^2 + 3x^2 +9x - 9x + 9) = (x^2 + 3) (x^2 - 3x + 3) (x^2 + 3x + 3)