Odpowiedzi

2009-12-06T23:10:02+01:00
A)
a2 = 5/12
a3 = 2/15
q = a3 : a2 =( 2/15)/(5/12) = (2/15)*(12/5) = 8/25
a2 = a1*q -----> a1 = a2 : q
a1 = [5/12]: (8/25) = [5/12]*[25/8] = 125/96

an = a1*q^(n-1) = [125/96]*[8/25]^(n-1)

b)
a2 = 7
a4 = 28
a4 = a2*q^2
q^2 = a4 : a2 = 28 : 7 = 4 = 2^2
q = 2
a2 = a1*q
7 = a1*2 ----> a1 = 7/2 = 3,5
an = a1*q^(n-1) = 3,5*2^(n-1)
---------------------------------------
gdzie q^2 - oznacza q do potęgi 2
2^(n-1) - oznacza 2 do potęgi o wykładniku n-1