text: sigma i= 1 to 15  [(i^2-2i)/n].....find the sum using the summation formulas? please do this in detail becasue i need help with this concept thnx what is n?  a variable? sum of i^2 from 1 to n is (n*(n+1)*(2n+1))/6 sum of i from 1 to n is n(n+1)/2 (i^2-2i)/n = (1/n)[i^2 - 2i] = (1/n)[(n*(n+1)*(2n+1))/6 - 2n(n+1)/2] = (1/n)[(n*(n+1)*(2n+1))/6 - n(n+1)] rplace n with 15 (1/n)[(15*(15+1)*(2*15+1))/6 - 15(15+1)] = (1/n)[(15*16*31)/6 - 15(16)] = (1/n)[1240 - 240] = (1/n)(1000) = 1000/n