SQLite Does index help when querying using the same column

CREATE INDEX idx_ex1 ON ex1(a,b,c);

select a,b from ex1 as res join ex2,ex3 where a=<somevalue> and b = <somevalue> and c =ex2.t  and c= ex2.r

Does indexing c help us in this scenario ? Do we need to write the SQL query in different way to get benefits of indexing in this scenario.?