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Rechner für komplexe Zahlen

Add, subtract, multiply and divide complex numbers, raise them to powers, find nth roots, and convert a + bi to polar form, with an Argand diagram.

Aktualisiert Geprüfte Beispiele: 7

Rectangular a + bi (j also works) or polar r∠θ; θ uses the angle unit from settings unless you add ° or rad
Ausprobieren
Ergebnis
11 − 2i
Ergebnis: 11 − 2i
Real part
11
Imaginary part
−2
Modulus |z|
11.1803398875
Argument (angle)
−10.3048464688
Polar form
11.18034 ∠ −10.304846°

z₁ × z₂ = 11 − 2i, which is 11.18034 ∠ −10.304846° in polar form.

Argand diagram (dashed: unit circle)

ReImz₁ = 3 + 4iz₂ = 1 − 2iresult = 11 − 2i
So wird gerechnet S

  1. Multiply out, using i² = −1

    (ac−bd)+(ad+bc) i=(3⋅1−4⋅(−2))+(3⋅(−2)+4⋅1) i=11−2i(ac - bd) + (ad + bc)\,i = (3\cdot1 - 4\cdot(-2)) + (3\cdot(-2) + 4\cdot1)\,i = 11 - 2i

  2. Polar form of the result

    11.18033989 ∠ −10.30484647∘11.18033989\,\angle\,-10.30484647^\circ

Über Rechner für komplexe Zahlen

A complex number z = a + bi has a real part a and an imaginary part b, where i² = −1. Addition, subtraction and multiplication work in rectangular form; division multiplies top and bottom by the conjugate of the divisor. Powers and roots use polar form, z = r(cos θ + i sin θ): De Moivre's formula raises the modulus r to the power n and multiplies the angle θ by n.

Electrical engineers use complex numbers for AC impedance and phasors, and algebra students meet them as roots of polynomials. The default multiplies (3 + 4i)(1 − 2i) = 3 − 6i + 4i − 8i² = 11 − 2i, whose modulus is √125 ≈ 11.1803.

Inputs can be rectangular (3 + 4i, with j accepted for i) or polar (2∠90). Angles follow the degree, radian or gradian setting, and the argument is given between −180° and 180°. The Argand diagram draws each number as an arrow from the origin.

Durchgerechnete Beispiele

(3 + 4i)(1 − 2i)

Operation
Multiply z₁ × z₂
z₁
3 + 4i
z₂
1 - 2i
Ergebnis
11 − 2i
Real part
11
Imaginary part
-2

Prüfquelle: 3 − 6i + 4i − 8i² = 11 − 2i (hand calculation; Python (3+4j)*(1-2j))

(3 + 4i) ÷ (1 − 2i)

Operation
Divide z₁ ÷ z₂
z₁
3 + 4i
z₂
1 - 2i
Ergebnis
−1 + 2i
Real part
-1
Imaginary part
2

Prüfquelle: Python (3+4j)/(1-2j) = (-1+2j)

Polar form of 3 + 4i

Operation
Convert to polar form
z₁
3 + 4i
Modulus |z|
5
Argument (angle)
53.1301023542

Prüfquelle: Python decimal: atan2(4, 3) in degrees via Machin-series arctangent (hp.py)

(1 + i)⁸

Operation
Power z₁ⁿ
z₁
1 + i
n
8
Ergebnis
16
Real part
16
Imaginary part
0

Prüfquelle: Python (1+1j)**8 = (16+0j); (√2)⁸ = 16 at angle 8 × 45° = 360°

Fragen

How do you multiply complex numbers?

Expand the brackets and replace i² with −1: (a + bi)(c + di) = (ac − bd) + (ad + bc)i. For (3 + 4i)(1 − 2i) that is (3 + 8) + (−6 + 4)i = 11 − 2i. In polar form the rule is shorter: multiply the moduli and add the angles, so 5∠53.13° × 2.236∠−63.43° = 11.18∠−10.30°.

How do you divide complex numbers?

Multiply the top and bottom by the conjugate of the divisor, which makes the denominator a real number. (3 + 4i)/(1 − 2i) = (3 + 4i)(1 + 2i)/(1² + 2²) = (3 + 6i + 4i + 8i²)/5 = (−5 + 10i)/5 = −1 + 2i. Division by 0 + 0i is undefined.

How do you convert a complex number to polar form?

The modulus is r = √(a² + b²) and the argument is θ = atan2(b, a), which picks the correct quadrant. For 3 + 4i, r = √(9 + 16) = 5 and θ ≈ 53.130°, so 3 + 4i = 5∠53.130°. Plain arctan(b/a) gives the wrong angle when the real part is negative: −3 − 4i has an argument of about −126.870°, not 53.130°.

What is De Moivre's theorem?

For z = r(cos θ + i sin θ) and a whole number n, zⁿ = rⁿ(cos nθ + i sin nθ). So (1 + i)⁸, with r = √2 and θ = 45°, equals (√2)⁸ = 16 at an angle of 8 × 45° = 360°, which is the real number 16. The same idea gives n evenly spaced nth roots: the cube roots of 8 are 2 and −1 ± 1.732051i, 120° apart.

What is the square root of −1?

The imaginary unit i, defined by i² = −1; −i is the other square root. Every negative number has two imaginary square roots, so √−4 = ±2i, and the principal root, the one with argument 90°, is 2i. Powers of i repeat every four steps: i, −1, −i, 1, then i again.

Wie genau arbeitet „Rechner für komplexe Zahlen“?

Die Genauigkeit hängt von Ihren Eingaben und den Annahmen der Methode ab. Die Dezimalrechnung nutzt 50 signifikante Stellen, doch Schätzungen, numerische Verfahren und Quelldaten können ungenauer sein. Die angezeigte Rundung beseitigt diese Grenzen nicht. Anhand unabhängiger Quellen geprüfte Rechenbeispiele: 7. Beispielsweise wird „(3 + 4i)(1 − 2i)“ anhand von 3 − 6i + 4i − 8i² = 11 − 2i (hand calculation; Python (3+4j)*(1-2j)) geprüft.

Woher stammt die Methode?

Wolfram MathWorld — Complex Number; Wolfram MathWorld — de Moivre's Identity.

Über diesen Rechner

z=a+bi=r(cos⁡θ+isin⁡θ)r=a2+b2,θ=atan2⁡(b,a)zn=rn(cos⁡nθ+isin⁡nθ)\begin{gathered} z = a + bi = r(\cos\theta + i\sin\theta) \\[4pt] r = \sqrt{a^2+b^2},\quad \theta = \operatorname{atan2}(b, a) \\[10pt] z^n = r^n(\cos n\theta + i \sin n\theta) \end{gathered}

Quellen

  1. Wolfram MathWorld — Complex Number
  2. Wolfram MathWorld — de Moivre's Identity

Anhand von Quellen geprüft

Dieser Rechner enthält 7 Rechenbeispiele mit Ergebnissen aus unabhängigen Quellen. Sie laufen in der Testsuite und können auch hier ausgeführt werden.

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