Question 1130997
use the arithmetic sequence formula:

{{{a[n]=a[1]+(n-1)d}}} where {{{a[n]}}} is nth term, {{{a[1]}}} is te first term, and {{{d}}} is the common difference

given:

{{{a[27]=-1/2}}}=>{{{n=27}}}

 {{{d=2}}} 

{{{-1/2=a[1]+(27-1)2}}}

{{{-1/2=a[1]+26*2}}}

{{{-1/2=a[1]+52}}}

{{{-1/2-52=a[1]}}}

{{{-1/2-104/2=a[1]}}}

{{{a[1]=-105/2}}}


so, your answer is: B.{{{-105/2}}}