Consider the arithmetic sequence presented in the table below. N 4 37 and An 16 115 what is the first term, a1, and the 22nd term of the sequence?

Verified Answer :

If I'm reading this correctly, the table is telling you that \(a_4=16\) and \(a_{37}=115\).

Because the sequence follows an arithmetic progression, there is a common difference \(d\) between terms such that

\(a_n=a_{n-1}+d\)

You can solve for \(a_n\) explicitly in terms of the first term \(a_1\) by recursively substituting the right side:

\(a_n=a_{n-1}+d\)
\(\implies a_n=a_{n-2}+2d\)
\(\implies a_n=a_{n-3}+3d\)
\(\implies\cdots\implies a_n=a_1+(n-1)d\)

Let's first find the common difference. You have

\(a_5=a_4+d\)
\(\implies a_6=a_5+d=a_4+2d\)
\(\implies a_7=a_6+d=a_5+2d=a_4+3d\)
\(\implies\cdots\implies a_{37}=a_{36}+d=\cdots=a_4+33d\)

Substituting in the terms of the sequence that you know, you get

\(115=16+33d\implies d=3\)

Now you can find the first term:

\(a_4=a_1+(4-1)d\implies 16=a_1+9\implies a_1=7\)

and the 22nd term:

\(a_{22}=a_1+(22-1)d=70\)