tlng jwabin+ cara ya .....

1.
U3=ar^2=18
U5=ar^4=162
U9=?

=>ar^4=ar^2.r^2
162=18.r^2
r^2=162/18
r^2=9
r=akar 9
r=3

sub r=3
ar^2=18
a.3^2=18
a.9=18
a=18/9
a=2

U9=ar^8
=2.3^8
=2.6561
=13122 (a)

2.
U1=4 => ar^0
U5=324 => ar^4
ar^4=ar^0.r^4
324=4.r^4
r^4=324/4
r^4=81
r =3 (jawabannya 3 karena 3^4 hasilnya 81)

S5= 4(3^5-1)/3-1
=4(243-1)/2
=4(242)/2
=968/2
=484 cm

insyaallah ini benar