Question 1142569
<pre>

__,__,__,__,__,__,<u>1/2</u>,__,__,<u>??</u>,__,__,__,__,__,<u> 6</u>,__,...


{{{a[n]=a[1]+(n-1)d}}}


{{{a[7]=a[1]+(7-1)d}}}

{{{1/2=a[1]+6d}}}


{{{a[14]=a[1]+(14-1)d}}}

{{{6=a[1]+13d}}}

So we have the system:

{{{system(6=a[1]+13d,1/2=a[1]+6d)}}}

Solve for a<sub>1</sub> in one of the equations and
substitute in the other to find d.  Then find d by 
substituting in the equation you got when you solved 
for d.  Then substitute the values n=10, along with 
what you got for a<sub>1</sub> and d.


Edwin</pre>