jumlah tujuh buah suku dari deret geometri 4+2+1+0,5+...

a = 4 ,r = 1/2
Sn = a(1-r^n )/1-r
= 4(1-(1/2)^7 )/1-1/2
= 4(1 - 1/128)/ 1/2
= 4(127/128)/ 1/2
= 127/32/ 1/2
= 127×2/32
= 254/32