Find the sum of the first n terms of sequence 1 / 2,1 / 4,1 / 8,1 / 16

Find the sum of the first n terms of sequence 1 / 2,1 / 4,1 / 8,1 / 16

a1=1/2,q=1/2
Sn=(1/2)[1-(1/2)^n]/[1-(1/2)]
=1-(1/2)^n