Question

Please help out

Answer 1

$a_1=-5;\ a_2=20;\ a_3=-80\\\\a_n=a_1r^{n-1}\\\\r=a_2:a_1\to r=20:(-5)=-4\\\\Answer:\boxed{a_n=-5\cdot(-4)^{n-1}}\to\fbox{B.}$