Question

If r is positive r>l, it is convenient to
write sn= a(r^n-1) ÷r-1​

Answer 1

Answer:

Yes, this is a convenient solution.

Step-by-step explanation:

Sum of Geometric series is given by

  S=a+a*r+a*(r^2)+to+a*(r^(n-1))

Multiplying both sides with r,

(r*S)=a*r+a*(r^2)+to+a*(r^(n-1))+a*(r^n)

since r>1,

      (r*S)>S

 So,

    (r*S)-S=a*(r^n)-a

   or, S(r-1)=a*(r^n-1)

   or, S= a*(r^n-1)/(r-1)