Question

find the value of a1 for an infinite geometric series with s=-45 and r=-1/3

 

Answer 1

Recall the formula

In geometric series sum of infinite terms = a/(1-r)

Here a = first term, r = common ratio.

r = -1/3, s = -45

Substitute the values in above formula.

-45 = a/(1-(-1/3))

-45 = a/(1+1/3)

Multiple to each side by (1+1/3)

-45(1+1/3) = [a/(1+1/3)]*(1+1/3)

-45-15 = a

-60 = a

a1 = -60