Chứng tỏ rằng:
a) Nếu \(\overline {cd} \vdots 4\) thì \(\overline {abcd} \vdots 4\)
b) Nếu \(\overline {abcd} \vdots 4\) thì \(\overline {cd} \vdots 4\)
Ta có:
\(\begin{array}{l}
\overline {abcd} = 100.\overline {ab} + \overline {cd} \\
= 4.25.\overline {ab} + \overline {cd}
\end{array}\)
a) Nếu \(\overline {cd} \vdots 4\) thì \(\overline {abcd} \vdots 4\)
b) Nếu \(\overline {abcd} \vdots 4\) thì \(4.25.\overline {ab} + \overline {cd} \vdots 4\) nên \(\overline {cd} \vdots 4\)
-- Mod Toán 6
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