Разложите на множители:

а) 16-1/81 х^4

б) 2 х+х^2+2 у-у^2

x^8 - y^8 = (x^4 - y^4) (x^4+y^4) = (x^2-y^2) * (x^2+y^2) (x^4 + y^4) = (x-y) (x+y) (x^2+y^2) * (x^2+y^4) a^8 - b^4 = (a^4 - b^2) (a^4 + b^2) = (a^2 - b) (a^2+b) (a^4 + b^2) a^9 - 1 = (a^3 - 1) (a^6+a^3 + 1) b^2-c^2 - b+c = (b-c) (b+c) - (b-c) = (b-c) (b+c-1) a + b - a^2 + b^2 = b^2 - a^2 + b + a = (b-a) (b+a) + 1 (b+a) = (b-a+1) (a+b)