Five roots

Algebra Level 5

The equation $x^5-2x^4-1=0$ has five complex roots $r_1, r_2, r_3, r_4, r_5$ . Find the value of $\frac{1}{r_1^8}+\frac{1}{r_2^8}+\frac{1}{r_3^8}+\frac{1}{r_4^8}+\frac{1}{r_5^8}.$