Question

tìm các giá trị nguyên của x để:

a/ 21 chia hết cho x+7

b/ -55 chia hết cho (x+2)

c/ 2x chia hết cho x-1.

GIÚP MIK VỚI!!!!!!

Answer 1

a/ \(21⋮x+7\)

\(\Leftrightarrow x+7\inƯ\left(21\right)\)

\(\Leftrightarrow\left[{}\begin{matrix}x+7=1\\x+7=21\\x+7=-1\\x+7=-21\end{matrix}\right.\)\(\Leftrightarrow\left[{}\begin{matrix}x=-6\\x=14\\x=-8\\x=-28\end{matrix}\right.\)

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b/ \(-55⋮x+2\)

\(\Leftrightarrow x+2\inƯ\left(-55\right)\)

\(\Leftrightarrow\left[{}\begin{matrix}x+2=-1\\x+2=1\\x+2=-55\\x+2=55\end{matrix}\right.\)\(\Leftrightarrow\left[{}\begin{matrix}x=-3\\x=-1\\x=-57\\x=53\end{matrix}\right.\)

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c/ \(2x⋮x-1\)

\(\Leftrightarrow x-1\inƯ\left(2x\right)\)

\(\Leftrightarrow\left[{}\begin{matrix}x-1=1\\x-1=-1\\x-1=2x\\x-1=-2x\end{matrix}\right.\) \(\Leftrightarrow\left[{}\begin{matrix}x=2\\x=0\\x=-1\\x=\dfrac{1}{3}\end{matrix}\right.\)

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