Question

Find an equation for the nth term
-4, -16, -64, -256, ...

Answer 1

$It's\ the\ geometric\ sequence:\\a_1=-4;\ a_2=-4\cdot4=-16;\ a_3=-16\cdot4=-64;\ a_4=-64\cdot4=-256\\\\a_n=a_1r^{n-1}\\\\a_1=-4;\ r=4\\\\a_n=-4\cdot4^{n-1}=-1\cdot4\cdot4^{n-1}=-4^n\\\\Answer:\boxed{a_n=-4^n}$