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(x^4-1)/20=4
x^4-1=80
x^4-81=0
(x^2)^2-9^2=0
(x^2-9)(x^2+9)=0
x^2-9=0 (x-3)(x+3)=0 x=3 y=-3
x^2+9=0 x^2=-9=(-3)^2 x=3i x=-3i