The terms -2, 1+2k, 4+4k... form an arithmetic sequence. If the sum of the first ten terms is a+bk then give the value of a-b.
I got up to finding the common difference (2k+3). I don't know what to do after.
I regret this post is wrong the given terms are in AP with common difference 2k+3. But with three variables a,b and k we need to have some more information to resolve the solution.