Assuming you need this to be able to truly recurse through n number of levels - here's an actual recursive version of it:

WITH testdata as (

select 1 as ID, 0.11 as A, cast(0 as float(53)) as B union all

select 2 as ID, 0.45 as A, 0.5 as B union all

select 3 as ID, 0.85 as A, 0.75 as B

),

recurseCTE as (

select id,a,b,1-a*(1-b) as interim

from testdata where ID=1

UNION ALL

select T.id,T.a,T.b,1-T.a*(1-T.b*r.interim) interim

from testdata T join RecurseCTE R on T.id=R.id+1

)

select *, 1-interim as F

from recurseCTE

where ID=(select max(ID) from testdata)