Question 898615
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Hi
Arithmetic : d = 3
{{{S[n]= (n/2)(2*a[1]+ (n-1)d) = 345}}}
{{{(n/2)(2*2+ 3n - 3) = 345}}}
{{{(n/2)(3n+1)= 345}}}
 3n^2 + n = 690
 3n^2 + n - 690 = 0
 *[invoke quadratic "x",3,1,-690]
n = 15 
{{{a[n]=a[1]+(n-1)*d}}}
 {{{a[15]= 2 +(14)*3 = 44}}}
   x = 44
check: 15(2 + 44)/2 = 345