1)4а-а^3=а(4-а²)=а(2-а)(2+а)
2)16-1/81 у4= (4-1/9у²)(4+1/9у²)=(2-1/3у)(2+1/3у)(4+1/9у²)
3)а+а^2-b-b^2=(а+b)+(a²-b²)=(a+b)+(a-b)(a+b)=(a+b)(1+a-b)
