Question

Дано: Sn=635. b1=5. q=2. n=?

Answer 1

Sn=b1(q^n-1)/q-1

 

635=5(2^n-1)/2-1

 

635=5*2^n-5

 

5*2^n=640

 

2^n=640/5

 

2^n=128

 

n=7, т.к.2^7=128