Question 1085483
1) What is a possible expression for the series
-6 -12 -24 -48 -96 -192<pre>That's a geometric series with a<sub>1</sub>=-6 and common ratio =r=2

{{{a[n]=-6*2^(n-1)=-3*2*2^(n-1)=-3*2^1*2^(n-1)=-3*2^(1+n-1)=-3*2^n}}}</pre>2) What is a possible expression for the series
-7 +12 -17 +22 -27<pre>
That would be an arithmetic series with a<sub>1</sub>=-7 and common 
difference = d = 5 if it weren't for the alternating signs.  So we
use the arithmetic series formula and multiply by the sign changing
factor (-1)<sup>n</sup>

{{{a[n] = (-1)^n*(7+(n-1)5)=(-1)^n*(7+5(n-1))=(-1)^n*(7+5n-5)=(-1)^n*(5n+2)}}}

Edwin</pre>