(13.) what is the first term if
the sum of the first 12 terms is
1,260 and the last term is 204?

the first term is 6

Step-by-step explanation:

We would apply the formula for determining the sum of n terms of an arithmetic sequence. It is expressed as

Sn = n/2(a + l)

Where

n represents the number of terms in the arithmetic sequence.

l represents the last term in the arithmetic sequence.

a represents the first term in the arithmetic sequence.

From the information given,

l = 204

n = 12

Sn = 1260

We want to determine a. Therefore,

1260 = 12/2(a + 204)

1260 = 6(a + 204)

a + 204 = 1260/6 = 210

a = 210 - 204 = 6