I've got a question regarding a mathematical problem I've been trying to solve.
How can I find the first term and the common rule of this arithmetic sequence with the following info:
The common difference ($d$) = $11$
The sum of the first 40 terms of the sequence = $8700$
So, how can I find the first term and the common rule of this sequence.
I hope I can get some help because I've been struggling trying to solve this problem for quite a while.
Best Answer
Hint: If the starting term were $0$, the sum of $40$ terms would be eleven times the sum of the numbers from $0$ to $39$. Can you do that? Then increasing the starting term by $1$ increases all the terms by $1$ and therefore the sum by $40$.