cara gerjain no7dan 8 kya mana kaka

U4 = a.r³

U4 = a.r³
U2 = a.r
54 = a.r³
6. = a.r ( dibagi )
9 = r²
r = √9
= 3

U4 = a.r³
54 = a.3³
54 = 27a
a = 2

U10 = a.r^9
= 2.3^9
= 39366
No.8
pola ke 6 = 1.2 + 2.2+ 3.2 + 4.2 +5.2 + 6.2 +21
pola ke 6 = 2+4+6+8+10+12+21
= 59