📘 functional analysis

1. **Problem statement:** We want to find the distance from the function $f(x) = x$ to the subspace $L$ spanned by $f_0(x) = 1$, $f_1(x) = \sin x$, and $f_2(x) = \cos x$ in the spa

1. **Stating the problem:** We explore the ideals of linear functionals in a Hilbert space, focusing on the concepts of numerical range and maximal ideals. 2. **Background and defi

1. The problem is to understand the concept of an ideal of a linear function in a Hilbert space, focusing on the numerical range and maximal ideal. 2. In a Hilbert space $\mathcal{

1. **Stating the problem:** We explore the ideals of a linear function in a Hilbert space, focusing on the numerical range and maximal ideals. 2. **Background and definitions:**

1. **Problem Statement:** We want to understand the ideal of a linear function in a Hilbert space, focusing on the numerical range and maximal ideals. 2. **Background:** In a Hilbe

1. **Stating the problem:** We have two nonempty, closed, convex sets $G$ and $H$ in a strictly convex Banach space $X$ with $G_0 \neq \emptyset$, where

1. **Problem Statement:** Prove that a Hilbert space $H$ is separable if and only if every orthonormal set in $H$ is countable. 2. **Definitions and Key Concepts:**

1. **Problem Statement:** Prove that a Hilbert space $H$ is separable if and only if every orthonormal set in $H$ is countable. 2. **Definitions and Key Concepts:**