Find all zeros of the polynomial?

Question

P(x)=x^4-81

Its zeros are
x_1= x_2= with x_1 x_3= + i with negative imaginary part and
x_4= + i with positive imaginary part.

Answer 1

x^4-81=0

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

x= 3, -3, 3i, -3i

Q.E.D.
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