How many terms are there in 2,4,8,16,....1024?
Clearly 2,4,8,16,...1024 form a G.P. with a=2 and r=4/2=2
Let the number of terms be n. Then
2x (2)power n-1=1024 or (2)power n-1=512=(2)power 9
n-1=9 or n=10.