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a20=(2*20-4)/(20+2)=36/22=18/11
(2n-4) /(n+2)=1
2n-4=n+2
n=6
odp. ; szóstym
2]
20-4n>0
-4n>-20
n<5
odp.: 4 wyraz; a1,a2,a3 i a4
3]
2x-3=(x+2-x-6)/2 /*2
4x-6=-4
4x=2
x=1/2
4]
a21=a1+20r
30=a1+20*0,7
a1=30-14=16
S21=[a1+a21]/2*21=[16+30]/2 *21=483
5]
a5=a1q^4=3*2^4=3*16=48
S5=a1*( 1-q^5)/(1-q)=3*(1-2^5) /(1-2)=3*(-31/-1)=93
6]
a8=a2+6r
54=-6+6r
6r=60
r=10
a2=a1+r
-6=a1+10
a1=-16