Question

Find the zeros

X^4-7x^2-144=0
The answer is x=4,−4,3i,−3i

Can someone help me with the steps

Answer 1

let u = x^2

then you have
u^2-7u-144 = 0
(u-16)(u+9) = 0
so u=16 or u=-9
that means that
x^2 = 16
x^2 = -9
ta-daaa!

Answer 2

x^4-7x^2-144=0

(x^2 - 16)(x^2 + 9) = 0
x^2 = 16
x = ± 4

or

x^2 = -9
x = ± 3i