Math Problem Statement

Find all complex numbers z that satisfy the equation Z*=2/z+i

Solution

We need to solve the equation:
zˉ=2z+i\bar{z} = \frac{2}{z} + i where zˉ\bar{z} represents the complex conjugate of zz.


Step 1: Represent the complex number zz

Let z=x+yiz = x + yi, where x,yRx, y \in \mathbb{R}.
Its complex conjugate is: zˉ=xyi.\bar{z} = x - yi. We substitute these into the equation.


Step 2: Substitute and rewrite the equation

The equation becomes: xyi=2x+yi+i.x - yi = \frac{2}{x + yi} + i. To simplify, multiply the numerator and denominator on the right-hand side by the complex conjugate of the denominator: 2x+yi=2(xyi)(x+yi)(xyi)=2(xyi)x2+y2.\frac{2}{x + yi} = \frac{2(x - yi)}{(x + yi)(x - yi)} = \frac{2(x - yi)}{x^2 + y^2}. Thus, the equation becomes: xyi=2xx2+y22yx2+y2i+i.x - yi = \frac{2x}{x^2 + y^2} - \frac{2y}{x^2 + y^2}i + i.


Step 3: Separate real and imaginary parts

The left-hand side is: xyi.x - yi. The right-hand side is: (2xx2+y2)+(i2yx2+y2i).\left(\frac{2x}{x^2 + y^2}\right) + \left(i - \frac{2y}{x^2 + y^2}i\right). Simplify the imaginary part: i2yx2+y2i=(12yx2+y2)i.i - \frac{2y}{x^2 + y^2}i = \left(1 - \frac{2y}{x^2 + y^2}\right)i. So the equation becomes: xyi=2xx2+y2+(12yx2+y2)i.x - yi = \frac{2x}{x^2 + y^2} + \left(1 - \frac{2y}{x^2 + y^2}\right)i.


Step 4: Equate real and imaginary parts

For the real parts: x=2xx2+y2.x = \frac{2x}{x^2 + y^2}. For the imaginary parts: y=12yx2+y2.-y = 1 - \frac{2y}{x^2 + y^2}.


Step 5: Solve the equations

Real part equation:

x(x2+y2)=2x.x(x^2 + y^2) = 2x. If x0x \neq 0, we can divide both sides by xx: x^2 + y^2 = 2. \tag{1}

Imaginary part equation:

y=12yx2+y2.-y = 1 - \frac{2y}{x^2 + y^2}. Using x2+y2=2x^2 + y^2 = 2 from Equation (1): y=12y2.-y = 1 - \frac{2y}{2}. y=1y.-y = 1 - y. This implies: 0=1,0 = 1, which is a contradiction unless y=0y = 0.


Step 6: Conclusion

Since y=0y = 0, the complex number zz must be purely real. From Equation (1): x2+02=2x2=2x=±2.x^2 + 0^2 = 2 \quad \Rightarrow \quad x^2 = 2 \quad \Rightarrow \quad x = \pm\sqrt{2}.

Thus, the solutions are: z=±2.z = \pm\sqrt{2}.


Final Answer

The complex numbers zz that satisfy the equation are: z=2andz=2.z = \sqrt{2} \quad \text{and} \quad z = -\sqrt{2}.


Do you want further details or have questions?


Related Questions:

  1. What is the definition of a complex conjugate?
  2. How do you simplify fractions with complex numbers?
  3. What is the geometric interpretation of the solutions z=2z = \sqrt{2} and z=2z = -\sqrt{2}?
  4. Can this method apply to other equations involving complex conjugates?
  5. How do we multiply and divide complex numbers?

Tip: Always equate the real and imaginary parts separately when working with complex equations.

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Math Problem Analysis

Mathematical Concepts

Complex Numbers
Algebraic Manipulation
Complex Conjugate

Formulas

z = x + yi, where x and y are real numbers
Complex conjugate: z* = x - yi
Multiplication of complex numbers: z1 * z2 = (a + bi)(c + di)
Real and imaginary parts of a complex number

Theorems

Equating real and imaginary parts in complex numbers
Properties of complex conjugates

Suitable Grade Level

Grades 11-12