phân tích đa thức thành nhân tử a) x^3+y(1-3x^2)+x(3y^2-1)-y^3 b)a^x+a^2y-7x-7y c)x(x+1)^2+x(x-5)-5(x+1)^2

$a)x^3+y.(1-3x^2)+x.(3y^2-1)-y^3_{}$

$x^3-3x^2y+3xy^2-y^3+y-x_{}$

$⇔(x-y)^3-(x-y)_{}$

$b)a^2x+a^2y-7x-7y_{}$

$⇔x.(a^2-7)+y.(a^2-7)_{}$

$⇔(a^2-7)(x+y)_{}$

$c)x.(x+1)^2+x(x-5)-5(x+1)^2_{}$ 

$⇔(x+1)^2.(x-5)+x.(x-5)_{}$

$⇔[ (x+1)(x-5)+x].(x-5).(x+1)_{}$

$⇔(x^2-3x-5)..(x-5)(x+1)_{}$