Question 742214




{{{Sn = a1(1-r^n) / (1-r)}}}........... In this equation, 
"{{{Sn}}}" is the sum of the geometric series, "{{{a[1]}}}" is the first term in the series, "{{{n}}}" is the number of terms and "{{{r}}}" is the ratio by which the terms increase

given:

{{{-3+ 1 -1/3 +1/9  }}}+..

the ratio by which the terms increase is {{{-1/3}}} (if you multiply first term by {{{-1/3}}} you get second term {{{1}}},if you multiply second term by {{{-1/3}}} you get {{{(1)(-1/3)=-1/3}}}, etc.)  

so, {{{r=-1/3}}}, {{{a[1]=-3}}} and {{{n}}}={ 1,2,3,.... }