The first term of an arithmetic sequence is -8. Find the 20th term if the sum of the first 20 terms is 790.
790==20/2 * [2*(-8) + 19D], solve for D
D==5 - this is the common difference
20th term ==[- 8 + 5 * (20 - 1) ]
==[- 8 + (5 * 19) ]
==[ - 8 + 95]
== 87 - the 20th term
Your sequence looks like this:
-8 , -3 , 2 , 7 , 12 , 17 , 22 , 27 , 32 , 37 , 42 , 47 , 52 , 57 , 62 , 67 , 72 , 77 , 82 , 87 , >>Number of terms = 20>>Total Sum == 790
