$A)5x-x=25+19$
$4x=44$
$x=44:4$
$x=11$
$B)x^{200}=x$
⇒$x^{200}-x=0$
⇒$x.(x^{199}-1)=0$
⇒\(\left[ \begin{array}{l}x=0\\x^{199}-1=0\end{array} \right.\)
⇒\(\left[ \begin{array}{l}x=0\\x^{199}=1 \end{array} \right.\)
⇒\(\left[ \begin{array}{l}x=0\\x^{199}=1^{199} \end{array} \right.\)
⇒\(\left[ \begin{array}{l}x=0\\x=1\end{array} \right.\)
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