Find the number of terms in the arithmetic series if the first term [tex]$a_1 = -3$[/tex], the last term [tex]$a_n = 44$[/tex], and the sum of the first [tex][tex]$n$[/tex][/tex] terms is 328.

[tex] n = [/tex]



Answer :

To determine the number of terms [tex]\( n \)[/tex] in the arithmetic series, we need to use the given values:
- The first term [tex]\( a_1 = -3 \)[/tex]
- The last term [tex]\( a_n = 44 \)[/tex]
- The sum of the first [tex]\( n \)[/tex] terms [tex]\( S_n = 328 \)[/tex]

The formula for the sum of the first [tex]\( n \)[/tex] terms of an arithmetic series is:

[tex]\[ S_n = \frac{n}{2} \cdot (a_1 + a_n) \][/tex]

Given [tex]\( S_n = 328 \)[/tex], [tex]\( a_1 = -3 \)[/tex], and [tex]\( a_n = 44 \)[/tex], we can plug these values into the formula and solve for [tex]\( n \)[/tex].

First, substitute the known values into the formula:

[tex]\[ 328 = \frac{n}{2} \cdot (-3 + 44) \][/tex]

Calculate the sum inside the parentheses:

[tex]\[ -3 + 44 = 41 \][/tex]

Thus, the equation becomes:

[tex]\[ 328 = \frac{n}{2} \cdot 41 \][/tex]

To isolate [tex]\( n \)[/tex], multiply both sides of the equation by 2:

[tex]\[ 656 = n \cdot 41 \][/tex]

Finally, divide both sides by 41:

[tex]\[ n = \frac{656}{41} \][/tex]

Simplify the fraction:

[tex]\[ n = 16 \][/tex]

Therefore, the number of terms in the arithmetic series is:

[tex]\[ n = 16 \][/tex]