(x-3a)(x-a)(x+a)(x+3a)=0
(x^2-9a^2)(x^2-a^2)=0
x^4-10a^2+9a^4=0
(xx-1)(xx-4)=k
x^4-5x^2+4-k=0
10a^2=5
a^2=1/2
a^4=1/4
9a^4=4-k
k=4-9a^4=4-9/4=7/4
(x-3a)(x-a)(x+a)(x+3a)=0
(x^2-9a^2)(x^2-a^2)=0
x^4-10a^2+9a^4=0
(xx-1)(xx-4)=k
x^4-5x^2+4-k=0
10a^2=5
a^2=1/2
a^4=1/4
9a^4=4-k
k=4-9a^4=4-9/4=7/4