Question 1204841
General formula for Tn the nth term in an geometric  progression is

{{{tn= a*r^(n-1)}}}

where a is the first term and  {{{r}}}    is the common ratio  and    {{{n  }}}  is the number of terms

1) 24,12,6,3...

24,12,6,3...  the common ratio is 12/24 =6/12 = 6/12 =1/2
a= 24

{{{tn= 24*(1/2)^(n-1)}}}

2) 0,-1/2,-1,-3/2...

0,-1/2,-1,-3/2...

-1/2-0 = -1-(-1/2) = (-3/2)-(-1)= -1/2

The difference between two consecutive terms is -1/2  = d 

The nth. term of an AP is

{{{tn= a+(n-1)*d}}} ,  a is first term and n the number of terms
a=0 , and d= -1/2

{{{tn = 0+(n-1)*(-1/2)}}}


{{{tn = (n-1)*(-1/2)}}}