Question

What is the correct answer?

Answer 1

x⁴ - 81  = x⁴ - 9² (Difference of 2 squares, then we an write it:


(x²-3)(x²+3) =0, → then (x²-3) = 0 and (x²+3)=0

(x²-3) = 0 → x² = 3 → x = +√3 and x = -√3
(x²+3) =0 → x² = -3 → x = +√-3  and x = -√3→ or  i√3 AND  x = -i√3

A{ -3 , +3 , -i√3 , i√3}