Guthaben nach 1 Jahr: G(1)= 1900*1,045
" 2 " : G(2)=(1900*1,045+1900)*1,045 = 1900*1,0452+1900*1,045=1900*(1,0452+1,045)
" 12 " : G(12)=1900*(1,04512+1,04511+1,04510+ ... +1,045)=1900*1,045(1,04511+1,04510+ ... +1)
=1900*1,045*1−1,0451−1,04512 =27481,66, weil
1+q+q2+q3+qn = 1−q1−qn+1, q≠1,n∈ℕ