The 15 th tern of ath arithmetic spquence is 21 and the cumnocau difference is -4 .
(x) Find the first term of the sequence.
(b) Find the 29:1s torm of the secquence.
© Piad the suan of the first 40 verms of the seqnence.

The formula for finding the nth term of an arithmetic sequence is given by , where is the first term, is the common difference, and is the term number. Given that the 15th term ( ) is 21 and the common difference ( ) is -4, we can set up the equation:

This simplifies to , leading to .

The formula for any term in an arithmetic sequence can help us find the 29th term:

Calculating gives .

To find the sum of the first 40 terms, use the formula:
.
First, find .
Thus, .

So, the first term is 77, the 29th term is -35, and the sum of the first 40 terms is -40.