arithmetic sequence

Question

An arithmetic sequence has t₁ = 3, t₂ = 10. Find t_n , S _n.

Answer 1

an arithmetic sequence is given by a_n = a₁ + (n-1)d where n is the number of terms and d is the difference.

In this case the difference is t₂-t₁=7 and a₁=3.

You should be able to plug numbers into the formula.

Oh, the sum = n(a₁+a_n)/2