Question

q=2 S4=45 надо найти b1 и b4 

Answer 1

b4=b1*q^3
S=b1*(q^4-1)/1=45
b1(2^4-1)=45
b1=3
b4=3*8=24

Answer 2

S4=b1(q^4-1) / q-1
15b1=45
b1=3
b4=b1*q^3=3*8=24