Question

Tìm x,y thuộc Z, biết : 

a) x + 4 chia hết x - 1

b) xy + x - y = 5

Answer 1

\(x+4⋮x-1\)

\(\Rightarrow x-1+5⋮x-1\)

      \(x-1⋮x-1\)

\(\Rightarrow5⋮x-1\)

\(\Rightarrow x-1\in U\left(5\right)\)

\(\Rightarrow x-1\in\left\{-1;1;-5;5\right\}\)

\(\Rightarrow x\in\left\{0;2;-4;6\right\}\)

vay___

\(xy+x-y=5\)

\(\Rightarrow x\left(y+1\right)-y=5\)

\(\Rightarrow x\left(y+1\right)-y+1=5+1\)

\(\Rightarrow\left(x-1\right)\left(y+1\right)=6\)

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