Teilsummen bilden:
a) 3/4*2*(2/5)^n = 3/2*(2/5)^n
geometrische Reihe: a0= (3/2*4/25) = 6/25, q= 2/5
Summe = 3/2* (6/25)/(1-2/5)= 3/2* 6/25*5/3= 2/5
b) 9/4*(-1/5)^n
a0= 9/4*(-1/5)^2 = 9/4*1/25= 9/100, q= -1/5
Summe: (9/100)/(1+1/5) = 9/100*5/6 = 3/40
Gesamtwert: 2/5+3/40 = 16/40+3/20 = 19/40 = 0,475