a) 9x^2 - x^6 = (3x)^2 - (x^3)^2 = (3x - x^3)*(3x + x^3) = x* (3-x^2)*x(3 + x^2)=
= x^2 *(3-x^2)*(3+x^2)
б) x^4-6x^2+9 = (х^2)^2 -2*3*x^2 + 3^2 = (x^2 -3)^2
