x^4-(a^2+9)x^2+9a^2=0
(x^2-9) (-(a-x)) (a+x) = 0
(x^2-9) (-(a^2-x^2)) = 0
x = -3
x = 3
x^4-х^2*a^2-9x^2+9a^2=0
(x^4-9x^2)-(х^2*a^2-9a^2)=0
x^2(x^2-9)-a^2(x^2-9)=0
(x^2-9)(x^2-a^2)=0
x^2-9 =0 или x^2-a^2=0
х = ±3 х=±а
