Tolong yaa . Terimakasih

N0.18
U2=3
a+b=3
U5=6
a+4b=6
a+b=3
Eliminasi a
3b=3
b=1
a+b=3
a+1=3
a=2
U9=a+8b=2+8.1=10
No. 19
a=-3
b=-5-(-3)=-5+3=-2
Un=a+(n-1)b
=-3+(n-1)(-2)
=-3-2n+2
=-1-2n
No. 20
a=-3
b=-2-(-3)=-2+3=1
Un=19
-3+(n-1)1=19
n-1=19+3
n=22+1
n=23
No. 21
U2=6
ar=6
U5=48
ar⁴=48
ar.r³=48
6.r³=48
r³=48/6
r³=2³
r=2
U6=U5.r
=48.2=96
No. 22
a=54
r=18/54=1/3
S~=a/1-r
=54/1-⅓
=54:⅔
=54.3/2=81