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Let $w = a + bi$ be a complex number and let $T : \mathbb C\to \mathbb C$ be defined by $T (z) = w \cdot z$. Considering $\mathbb C$ as a vector space over $\mathbb R$, find the matrix $B$ representing $T$ relative to the basis $\{1, i\}$ of $\mathbb C$.

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    What did you try?2012-12-08

1 Answers 1

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Applying $T$ on the basis:

$T(1)=w=a\cdot 1+b\cdot i=(a,b)$

and $T(i)=w\cdot i=(a+bi)\cdot i=a\cdot i -b\cdot 1=(-b,a).$

So $T=\begin{pmatrix}a & -b \\ b &a\end{pmatrix}.$

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    Note that the matrices of this form provide a concrete construction of the complex numbers.2012-12-08