Question 980366
r, common ratio.
{{{4/9=r^2}}}, and then {{{9r^3=b}}}.


You can finish from the term at index 1 or from the term at index 3.  You want the POSITIVE value for r.


{{{r^2=4/9}}}
{{{r=0+- 2/3}}}
{{{r=2/3}}}


Easiest enough to continue from index of term 3.
{{{4*(2/3)=highlight(8/3=t[4])=b}}}.