Answer:
Tn = Tn-1 + 2(n-1) + 5
Kindly note that Tn-1 means T subscript n-1
Explanation:
Here, we want an expression for the nth term.
First term is 7
Then first common difference is 7
second common difference is 7 + 2
Third common difference is 9 + 2
So within the common differences, the nth term is 7 + (n-1) 2
Now, the nth term of the series would be;
Tn = Tn-1 + 7 + 2(n-1)
Tn = Tn-1 + 7 + 2n -2
Tn = Tn-1 + 2n + 5
Now there is a fix to this,
n for the term is not the same n for the common difference.
the 7th term works with the 6th common. difference, while the 8th term work for the 7th common difference.
So we might need to rewrite the final expression as follows;
Tn = Tn-1 + 2(n-1) + 5