Square of Complex Number
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Theorem
Let $z = a + i b$ be a complex number.
Then its square is given by:
- $z^2 = a^2 - b^2 + i \paren {2 a b}$
Proof
\(\ds z^2\) | \(=\) | \(\ds \paren {a + i b}^2\) | by hypothesis | |||||||||||
\(\ds \) | \(=\) | \(\ds \paren {a + i b} \paren {a + i b}\) | Definition of Square Function | |||||||||||
\(\ds \) | \(=\) | \(\ds \paren {a \times a - b \times b} + i \paren {a \times b + b \times a}\) | Definition of Complex Multiplication | |||||||||||
\(\ds \) | \(=\) | \(\ds a^2 - b^2 + i \paren {2 a b}\) | simplification |
$\blacksquare$
Sources
- 1964: Milton Abramowitz and Irene A. Stegun: Handbook of Mathematical Functions ... (previous) ... (next): $3$: Elementary Analytic Methods: $3.7$ Complex Numbers and Functions: Powers: $3.7.18$