a)
a_1=\frac{7-4}{12}=\frac{1}{4}
a_2=\frac{7-8}{12}=-\frac{1}{12}
r=a_2-a_1=-\frac{1}{12}-\frac{1}{4}=-\frac{1}{12}-\frac{3}{12}=-\frac{1}{3}
b)
b_2=2
S_3=6
x,2,y wyrazy ciągu geometrycznego
tw. a_n^2=a_{n-1}*a_{n+1}
2^2=x*y
4=xy
x=\frac{4}{y}
x+2+y=6
\frac{4}{y}+2+y=6
\frac{4}{y}+y-4=0/*y
y^2-4y+4=0
(y-2)^2=0
y=2
x=2
q=1