Ellipse.

Conic sections.

Geometry, Projective.

Operator theory > General theory of linear operators > General (adjoints, conjugates, products, inverses, domains, ranges, etc.)

Operator theory > General theory of linear operators > Numerical range, numerical radius.

Functions of a complex variable > Function theory on the disc > Blaschke products.

Linear and multilinear algebra; matrix theory > Research exposition (monographs, survey articles)

Linear and multilinear algebra; matrix theory > Basic linear algebra > Norms of matrices, numerical range, applications of functional analysis to matrix theory.

Geometry > Research exposition (monographs, survey articles)

Geometry > Real and complex geometry > Elementary problems in Euclidean geometries.

Geometry > Analytic and descriptive geometry > Questions of classical algebraic geometry.