Question 1086467
1) determine the sum of the arithmetic series 19.5+14+8.5+...t24
<pre>
t2-t1 = 14-19.5 = -5.5 = d
t3-t2 =  8.5-14 = -5.5 = d

{{{S[n]=expr(n/2)(2t[1]+(n-1)d)}}}

Substitute n = 24, t<sub>1</sub> = 19.5, and d = -5.5,
to find S<sub>24</sub> 

</pre>
2)Determine the value of t1 for an arithmetic sequence, 
  where d=-4 and S14 = 1120
<pre>
{{{S[n]=expr(n/2)(2t[1]+(n-1)d)}}}

Substitute n = 14, d = -4, then substitute S<sub>14</sub> = 1120. 

Then solve for t<sub>1</sub>.

Edwin</pre>