共轭复数

共轭复数

对于复数

z

,

w

{\displaystyle z,w}

z

+

w

¯

=

z

¯

+

w

¯

z

w

¯

=

z

¯

w

¯

z

w

¯

=

z

¯

w

¯

(

z

w

)

¯

=

z

¯

w

¯

(

w

0

)

z

¯

=

z

(

z

R

)

z

n

¯

=

z

¯

n

(

n

Z

)

|

z

¯

|

=

|

z

|

|

z

¯

|

2

=

z

z

¯

(

z

¯

)

¯

=

z

z

1

=

z

¯

|

z

|

2

(

z

0

)

{\displaystyle {\begin{array}{l}{\overline {z+w}}={\overline {z}}+{\overline {w}}\\{\overline {z-w}}={\overline {z}}-{\overline {w}}\\{\overline {zw}}={\overline {z}}\,{\overline {w}}\\{\overline {\left({\dfrac {z}{w}}\right)}}={\dfrac {\overline {z}}{\overline {w}}}&(w\neq 0)\\{\overline {z}}=z&(z\in \mathbb {R} )\\{\overline {z^{n}}}={\overline {z}}^{n}&(n\in \mathbb {Z} )\\|{\overline {z}}|=|z|\\|{\overline {z}}|^{2}=z{\overline {z}}\\{\overline {({\overline {z}})}}=z\\z^{-1}={\dfrac {\overline {z}}{|z|^{2}}}&(z\neq 0)\end{array}}}

一般而言,如果复平面上的函数

ϕ

{\displaystyle \phi }

能表为实系数幂级数,则有:

ϕ

(

z

¯

)

=

ϕ

(

z

)

¯

{\displaystyle \phi ({\overline {z}})={\overline {\phi (z)}}}

最直接的例子是多项式,由此可推得实系数多项式之复根必共轭。此外也可用于复指数函数与复对数函数(取定一分支):

exp

(

z

¯

)

=

exp

(

z

)

¯

log

(

z

¯

)

=

log

(

z

)

¯

(

z

0

)

{\displaystyle {\begin{array}{l}\exp({\overline {z}})={\overline {\exp(z)}}\\\log({\overline {z}})={\overline {\log(z)}}&(z\neq 0)\end{array}}}

透过欧拉公式,在极坐标表法下,复数共轭可以写成

r

e

i

θ

¯

=

r

e

i

θ

{\displaystyle {\overline {re^{i\theta }}}=re^{-i\theta }}


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