find all zeroes -3x^4 + 27x^2 + 1200 =0

Answer 1

divide each term by -3

x^4 - 9x^2 - 400 = 0
(x^2 - 25)(x^2 + 16) = 0
x^2 = 25 OR x^2 = -16

x = ± 5 or x = ± 4i