What is the sum of the first five terms of a geometric series with a1 = 20 and r = 1/4?

 The required sum of first terms of the series is

Step-by-step explanation:  We are given to find the sum of the first five terms of a geometric series with first term and common ratio as follows :

We know that

the sum of first n terms of a geometric series with first term and common ratio r is given by

Therefore, the sum of first 5 terms of the given geometric series is given by

Thus, the required sum of first terms of the given geometric series is

-10i^2-4i

step-by-step explanation:

evaluate for p=2,q=5i

(2−4)(2+5i)i

(2−4)(2+5i)i

=−10i2−4i