An infinite geometric series has common ratio -1/2 and sum 45. What is the first term of the series?
Using the sum of an infinite series, we have :
a1 / [ 1 - r ] = the sum
Where a1 is the first term and r is the common difference.....so we have...
a1 / [ 1 - (-1/2) ] = 45 simplify
a1 / [ 3/2] = 45
a1 = 45 (3/2)
a1 = 67.5
Thank you, CPhill! Perfect!
+885 
