Question 1115681
Make A the subject of the formula {{{Sn=(Ar(r^n-1))/(r-1)}}}
distribute r
{{{Sn=(A(r^(n+1)-r))/(r-1)}}}
multiply both sides by (r-1)
{{{A(r^(n+1)-r)}}}  = {{{Sn(r-1)}}}
divide both sides by {{{r^(n+1)-r}}}
A = {{{Sn(r-1)/(r^(n+1)-r))}}}


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