Hello, now let me answer the above questions for you. What is the concept of neighborhood? What is neighborhood? I believe many friends still don't know. Now let's have a look!
1, the definition of mathematical analysis Any open interval centered on a is called the neighborhood of point A, and it is denoted as U(a). If δ is an arbitrary positive number, then (a-δ, a+δ) in the open interval is a neighborhood of point A, which is called δ neighborhood of point A and denoted as U(a, δ) = x <; a+δ} .p = " " & gt& lt/x & lt； a+δ} .& gt
2. Point A is called the center of this neighborhood, and δ is called the radius of this neighborhood.
3. After the center A is removed, the δ neighborhood of A is called the centripetal δ neighborhood of point A, sometimes the open interval (a-δ, A) is called the left δ neighborhood of A, and the open interval (a, a+δ) is called the right δ neighborhood of A. ..
4. Topology is defined as a subset of topological space (x, τ), with point x ∈ a.
5. If there is a set U, it is satisfied that ①U is an open set, that is, U∈τ, ② Point x∈U, ③U is a subset of A, then point X is the interior point of A and A is the neighborhood of point X. ..
6. If A is an open (closed) set, it is called an open (closed) neighborhood.