Describe Geometrically The Sets Of Points Z In The Complex P
Describe Geometrically The Sets Of Points Z In The Complex Plane Defin
Analyze and interpret geometrically the sets of points \(z\) in the complex plane defined by the following relations: (1) \(|z - z_1| = |z - z_2|\) where \(z_1, z_2 \in \mathbb{C}\). (2) \(1/z = z\). (3) \(\operatorname{Re}(z) = 3\). (4) \(\operatorname{Re}(z) > c\), (resp., \(\geq c\)) where \(c \in \mathbb{R}\). (5) \(\operatorname{Re}(az + b) > 0\) where \(a, b \in \mathbb{C}\). (6) \(|z| = \operatorname{Re}(z) + 1\). (7) \(\operatorname{Im}(z) = c\) with \(c \in \mathbb{R}\). Additionally, describe the properties of the inner products: the usual inner product \(\langle \cdot, \cdot \rangle\) in \(\mathbb{R}^2\) and the Hermitian inner product \((\cdot, \cdot)\) in \(\mathbb{C}\), and demonstrate that \(\langle z, w \rangle = \frac{1}{2}[(z,w) + (w,z)] = \operatorname{Re}(z,w)\), where \(z, w \in \mathbb{C}\), with the identification \(z = x + iy \in \mathbb{C}\) corresponding to \((x, y) \in \mathbb{R}^2\).
Paper For Above instruction
Understanding geometric sets in the complex plane provides profound insights into complex analysis and its applications. Each of the given relations characterizes a particular geometric locus, such as lines, circles, or regions, revealing structural properties of complex points \(z = x + iy\). This paper explores these sets systematically, alongside a discussion of the properties of two inner products—one in \(\mathbb{R}^2\) and a Hermitian inner product in \(\mathbb{C}\)—as well as their interrelation.
1. The locus of points equidistant from two points: \(|z - z_1| = |z - z_2|\)
This relation describes the set of points \(z\) in the complex plane equidistant from two fixed points \(z_1, z_2 \in \mathbb{C}\). Geometrically, this set corresponds to the perpendicular bisector of the segment joining \(z_1\) and \(z_2\). To see this, note that \(|z - z_1| = |z - z_2|\) implies that \(z\) is located symmetrically with respect to the midpoint of \(z_1\) and \(z_2\), forming a straight line perpendicular to the segment connecting the two points—this is a classic locus of points equidistant from two points. When expressed explicitly, if \(z_k = x_k + iy_k\), the locus satisfies the linear equation obtained from the equality of Euclidean distances, resulting in a straight line in \(\mathbb{R}^2\).
2. The set of points satisfying \(1/z = z\)
This relation simplifies to \(z^2 = 1\), which yields the solutions \(z = \pm 1\). Geometrically, these solutions represent two distinct points on the real axis in the complex plane. The set therefore consists of exactly two points: \(-1\) and \(1\). Thus, this relation describes a discrete set of points rather than a continuous locus.
3. The vertical line where \(\operatorname{Re}(z) = 3\)
The condition \(\operatorname{Re}(z) = 3\) describes a vertical line in the complex plane at \(x=3\). All points \(z = x + iy\) with \(x=3\), where \(y\) traverses \(\mathbb{R}\), belong to this set. Geometrically, it is an infinite straight line parallel to the imaginary axis, indicating a locus of points with a constant real part.
4. The half-plane \(\operatorname{Re}(z) > c\) and \(\operatorname{Re}(z) \geq c\)
These sets describe the open and closed half-planes to the right of the vertical line \(x=c\). For \(\operatorname{Re}(z) > c\), the locus encompasses all points with real part strictly greater than \(c\), forming an open half-plane. When including the boundary points with \(\operatorname{Re}(z) = c\), it becomes a closed half-plane. These are fundamental in complex analysis for defining domains of holomorphic functions and for various boundary value problems.
5. The set where \(\operatorname{Re}(az + b) > 0\) for \(a, b \in \mathbb{C}\)
This relation involves a linear transformation of \(z\) followed by a real part condition. The transformation \(w = az + b\) can be viewed as a combination of rotation, scaling, and translation in \(\mathbb{C}\). The inequality \(\operatorname{Re}(w) > 0\) defines a right half-plane in the \(w\)-plane, and composing the inverse transformation maps this half-plane back into a half-plane in the \(z\)-plane. The geometric locus is therefore a half-plane bounded by the line \(\operatorname{Re}(az + b) = 0\), which itself is a straight line in the complex plane, unless \(a=0\), in which case the set is either empty or all points depending on the constants.
6. The relation \(|z| = \operatorname{Re}(z) + 1\)
This equation defines a locus involving both the modulus and the real part of \(z\). Substituting \(z = x + iy\), we get \(\sqrt{x^2 + y^2} = x + 1\). Squaring both sides results in \(x^2 + y^2 = (x + 1)^2\), which simplifies to \(x^2 + y^2 = x^2 + 2x + 1\), leading to \(y^2 = 2x + 1\). This is a parabola opening to the right, with its vertex at \((-0.5, 0)\). Therefore, the locus is a parabola in the complex plane representing the set of points where the modulus equals the shifted real part.
7. The line \(\operatorname{Im}(z) = c\)
Fixing the imaginary part of \(z\) to \(c\) describes a horizontal line in the complex plane at \(y = c\). All points \(x + ic\), with \(x \in \mathbb{R}\), lie on this line. This is a fundamental geometric object, frequently used as a boundary or domain in complex analysis, with constant imaginary part.
Inner products in \(\mathbb{R}^2\) and \(\mathbb{C}\)
The standard inner product in \(\mathbb{R}^2\) is defined by \(\langle Z, W \rangle = x_1 x_2 + y_1 y_2\) for \(Z = (x_1, y_1)\) and \(W = (x_2, y_2)\). The Hermitian inner product in \(\mathbb{C}\) is given by \((z, w) = zw\), which generally is not symmetric. The key property to consider is the relation \(\langle z, w \rangle = \frac{1}{2}[(z,w) + (w,z)]\), which corresponds to the real part of the Hermitian inner product: \(\operatorname{Re}(z,w)\). When identifying \(z = x + iy\), the inner products link the algebraic operations in \(\mathbb{C}\) with geometric interpretations in \(\mathbb{R}^2\), illustrating the deep connection between complex analysis and Euclidean geometry.
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