Find the sum of the products of the corresponding terms of the sequences 2,4 , `8,16,32` and `128,32,8,2, 1/2`

Explanation

The sequence is `2 xx 128,4 xx 32,8 xx 8,16 xx 2,32 xx 1/2`

i.e.: `256,128,64,32,16 therefore a=256, r=128/256=1/2`

`n=5 , S_5=a (1-1/2^5)/1-1/2=256(31/32/1/2)=256 xx 31/32 xx 2=16 xx 31=496`