Answer:
x = - 1 or 1 or -4 or 4
Step-by-step explanation:
x^4 - 17x^2 + 16 = 0
let y = x^2
y^2 -17y + 16 = 0
(y-16)(y-1) = 0
y = 16 or y = 1
x^2 = 16 or x^2 = 1
x^2 = 16: x = 4 or -4
x^2 = 1: x = 1 or -1
