a) wyraz srodkowy jest suma wyrazow stojacych obok niego i podzielonych przez 2 dlatego:
(x - 4 + x + 12) / 2 = 5
(2x + 8) / 2 = 5
x+4=5 /-4
x=1
b) a1 = 6
a5 = 9
a5 =a1 + 4r
9 = 6 + 4r | - 6
3 = 4r | : 4
r = 3/4
a2 = x =a1 + r = 6 + 3/4 = 6 i 3/4
a3 = y = a2 +r = 6 i 3/4 + 3/4 =7 i 1/2
a4 = z = a3 + r= 7 i 1/2 +3/4 =7 i 2/4 +3/4 =8 i 1/4
