Solve the polynomial equation by finding all real roots

Question

g(x) = x^4 + 15x^2 -16
SO:
(X^2+16) (X-1)....I'M STUCK
THANKS

Answer 1

you factored incorrectly, expand your answer, you won't get the original

x^4 + 15x^2 -16 = 0
(x-1)(x^3 + x^2 + 16x + 16) = 0
so x = 1
or
x^3 + x^2 + 16x + 16 = 0
by grouping
x^2(x+1) + 16(x+1) = 0
(x+1)(x^2 + 16) = 0
so we have a double root at x=1
and
x^2 = -16
x = ± √-16 = ± 4i , but those are not real, so
all you have in real roots is
x = 1