а) 48, 12,...

b1 = 48,  q = 1/4

b6 = b1*q^5 = 48/4^5 = 3/64

bn = b1*q^(n-1) = 48/4^(n-1) = 3*(4^(3-n))

б) 64/9, -32/3...

b1 = 64/9,  q = - 3/2

b6 = b1*q^5 = - 64*243/(9*32) = -54

bn = b1*q^(n-1) = (64/9)*(-3/2)^(n-1)

в) -0,001; -0,01...

b1 = -0,001;  q = 10

b6 = b1*q^5 = -0,001*10^5 = -100

bn = b1*q^(n-1)= -0,001* 10^(n-1) = -10^(n-4) 

г) -100,  10....

b1= -100;  q = -0,1

b6 = b1*q^5 = 100 *(-10)^(-5) = -0,001

bn = b1*q^(n-1) = 100*(-0,1)^(n-1)