Question 974742
a, ar, ar^2, ar^3, -2, ar^5, -8, ....


{{{-2*r^2=-8}}}
{{{r^2=4}}}
{{{r=-2}}}  or  {{{highlight_green(r=2)}}}.


{{{ar^4=-2}}}
{{{a=-2/r^4}}}
{{{a=-2/16}}}
{{{highlight(a=-1/8)}}}