if a +1/a + 2 = 0, then the value of a^15-1/(a^100) is :

if $a +\frac{1}{a} + 2 = 0$,

then the value of $a^{15}-\frac{1}{a^{100}}$

if $a +\frac{1}{a} + 2 = 0$,

Then, $a -\frac{1}{a} = -2$, 

Put the value of a = -1

$a^{15}-\frac{1}{a^{100}}$ = $-1^{15}-\frac{1}{-1^{100}}$ = -2