if A belongs to B then show that B' belongs to A'

dear student

let's prove this using sets

universal set U={1,2,3,4,5,6,7,8}

let B={1,2,3,4,5}

and A={1,2}

then A belongs to B

A'={3,4,5,6,7,8}

B'={6,7,8}

clearly B' is a subset of A'

regards