tentukan jumlah setiap deret geometri berikut a. 2+6+28+54+162+...+U7 b.3+15+75+...+U6 c.1+4+16+64+...+U7 d.5+10+20+40+80+...+U8 e.¼+½+1+2+...+U10

a.) a = 2
r = 3
Sn = a ( r^n - 1 ) / ( r - 1 )
S7 = 2 ( 3^7 - 1 ) / ( 3 - 1 )
= 2 ( 2187 - 1 ) / 2
S7 = 2186

b.) a = 3
b = 5
S6 = 3 ( 5^6 - 1 ) / ( 5 - 1 )
= 3( 15625 - 1 ) / 4
= 3( 3906 )
= 11.718

c.) a = 1
b = 4
S7 = 1 ( 4^7 - 1 ) / ( 4 - 1 )
= ( 16384 - 1 ) / 3
= 5461

d.) a = 5
b = 2
S8 = 5 ( 2^8 - 1 ) / ( 2 - 1 )
= 5 ( 256 - 1 ) / 1
= 5 ( 255 )
= 1275

e.) a = 1/4
b = 2
S10 = 1/4 ( 2^10 - 1 ) / ( 2 - 1 )
= 1/4 ( 1024 - 1 ) / 1
= 1/4 ( 1023 )
= 255 3/4