Question 864515
{{{S[n]= (n/2)(2*a[1]+ (n-1)d)}}}
{{{S[n]= (n/2)(160+ (n-1)2) = 710}}}
{{{S[n]= (n/2)(2n + 158) = 710}}}  
        n^2 + 79n - 710 = 0  Check Your numbers