How do you find the nth term and the total sum of the quadratic sequence 10, 20, 40, 70 etc? Thank you!
-
a[n] = 10 + 5n(n-1)
Sum(n) = 10n - 5(n+1)n/2 + 5(n+1)(2n+1)n/6
Sum(n) = 10n - 5(n+1)n/2 + 5(n+1)(2n+1)n/6
-
10, 20, 40, 70
_10_20__30 a_n - a_(n-1) = 10
a_n = a_(n-1) +a_(n-2) +10
S_n = 2(a_n) [a_n = the sum of the previous numbers in your series]
_10_20__30 a_n - a_(n-1) = 10
a_n = a_(n-1) +a_(n-2) +10
S_n = 2(a_n) [a_n = the sum of the previous numbers in your series]