The first term of the sequence is 77, the 29th term of the sequence is -35 and the sum of the first 40 terms of the sequence is -40.
Given that, [tex]a_{15} =21[/tex] and d=-4.
What is the nth term of the arithmetic sequence?
The nth term of the arithmetic sequence is [tex]a_{n} =a+(n-1)d[/tex].
To find the first term of the sequence:
[tex]a_{15}[/tex]=a+(15-1)(-4)
⇒21=a+(15-1)(-4)
⇒a=77
To find the 29th term of the sequence:
[tex]a_{29}[/tex]=77+(29-1)(-4)=-35
To find the sum of the first 40 terms of the sequence:
The first n terms of a sequence [tex]=\frac{n}{2}[2a+(n-1)d)][/tex]
[tex]S_{40} =\frac{40}{2}[2 \times77+(40-1)(-4))][/tex]
=20(154-156)=-40
Therefore, the first term of the sequence is 77, the 29th term of the sequence is -35 and the sum of the first 40 terms of the sequence is -40.
To learn more about the arithmetic sequence visit:
https://brainly.com/question/15412619.
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