If x+1/x= 2 cos θ, then x^3 +1/(x^3)=?

If $x+\frac{1}{x}= 2 cos θ$,

then $x^3 +\frac{1}{x^3}=$?

Put cosθ = 0^o 

cos0^o  = 1

then, 

 $x+\frac{1}{x}= 2$

$x^3 +\frac{1}{x^3}=$ 2³ - 2 × 3 = 2

Satisfy from the options = 2 cos 3θ = 2cos0^o  = 2 satisfied.

So the value of $x^3 +\frac{1}{x^3}$ = 2 cos 3θ