If A={x:x is a multiple of 3 } and B={x:x is a multiple of 5 } , then A−B is
A ∩ ¯B .
A={x:x is a multiple of 3}
⇒A={3,6,9….}
and B={x:x is a multiple of 5}
⇒B={5,10,15….}
Since A−B=A–(A∩B)=(A∩¯B)
or we can say A–B={x:x is a multiple of 3 but not a multiple of 5}