Odpowiedzi

2010-01-06T20:57:42+01:00
A₅=a₁+4r <=> a₁=a₅-4r
a₉=a₁+8r <=>a₁=a₉-8r
a₅-4r=a₉-8r

-8-4r=-2-8r
-4r+8r=-2+8
4r=6/4
r=3/2
r=1½