deret geometri 1/2 , 1/4 , 1/8 , 1/16 .... a. U9 ? b. S9 ?

a= 1/2
r= 1/2
u9= a x r^n-1
=1/2 x 1/2 ^9-1
=1/2 x 1/256
=1/512
s9= a(1-r^n)/1-r
= 1/2(1-1/2^9)/1-1/2
=1/2 (1-1/512)/1/2
=2x1/2x511/512
=511/512