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\documentclass[a4paper]{jarticle}
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\setlength{\textheight}{46\baselineskip}
\setlength{\textwidth}{47zw}

\def\vect#1{\mbox{\boldmath $#1$}}

\usepackage{amsmath,amssymb}
%\usepackage{bm}
%\usepackage{graphicx}
\usepackage{ascmac}

\begin{equation*}
\prod_{i=1}^{k}(A-\mu_i I)X=0\Rightarrow (A-\mu_1 I)Y=0
\end{equation*}