Question

(x+3)(x^2-3x+9)+x(3-x)(3+x)=0

Answer 1

$(x+3)(x^2-3x+9)+x(3-x)(3+x)=0\\(x+3)(x^2-3x+9)+x(3-x)(x+3)=0\\(x+3)((x^2-3x+9)+x(3-x))=0\\(x+3)(x^2-3x+9+3x-x^2)=0\\(x+3)*9=0\\x+3=0\\x=-3$