An infinite geometric series has common ratio 1/3 and sum 25. What is the second term of the sequence?
S∞ = a1 / (1-r)
25 = a1 /(1-1/3)
25 * 3/2 = a1 = 37.5 Not possible (already greater than the sum) ratio must be MINUS 1/3
S = a1/(1 - -1/3)
25 * 3/4 = a1 = 75/4 75/4 (-1/3) = -75/12 is the second term (- 6.25)
