I think 'will be doubled' and 'will double' has the same meaning, like
The cost will be doubled
The cost will double
They are the same setnece, isn't it?
And one more thing, if there is specific time in future tense, should I
use only future perfect?
The cost will have been doubled by the end of this year.
or, just simple futre is ok?
The cost will be doubled by the end of this year.
Always appreciate your help.