Answer: [tex]S_n = -7.25 + 0.5(n - 1)[/tex]
Explanation: Let's form the arithmetic progression. For the sequence, not the sum, we use this form:
[tex]S_n = a + (n - 1)d[/tex], a is the first term and d is the common difference.
Now each term goes up by 0.5, so d is 0.5
Substituting everything in, we get:
[tex]S_n = -7.25 + (n - 1)(0.5)[/tex]
and we can verify this is true if we substitute n = 2, for -6.75 and so on.
