Question 1062804
{{{matrix(1,9,

matrix(1,2,second,term)/matrix(1,2,first,term),
""="",
matrix(1,3,1/9,"÷",-1/3),
""="",
matrix(1,3,1/9,"×",-3/1),
""="",
-3/9,
""="",
-1/3)}}}

{{{matrix(1,9,

matrix(1,2,third,term)/matrix(1,2,second,term),
""="",
matrix(1,3,-1/27,"÷",1/9),
""="",
matrix(1,3,-1/27,"×",9/1),
""="",
-9/27,
""="",
-1/3)}}}

{{{matrix(1,9,
matrix(1,2,fourth,term)/matrix(1,2,third,term),
""="",
matrix(1,3,1/81,"÷",-1/27),
""="",
matrix(1,3,1/81,"×",-27/1),
""="",
-27/81,
""="",
-1/3)}}


So {{{r =-1/3}}}

{{{a[n]}}}{{{""=""}}}{{{a[1]r^(n-1)}}}

{{{a[n]}}}{{{""=""}}}{{{expr(-1/3)(-1/3)^(n-1)}}}

{{{a[n]}}}{{{""=""}}}{{{(-1/3)^1(-1/3)^(n-1)}}}

{{{a[n]}}}{{{""=""}}}{{{(-1/3)^n}}}
Edwin</pre>