Question

Tìm x,y thuộc N 

4x-xy=15

Answer 1

Ta có: \(4x-xy=15\)

\(\Rightarrow x\left(4-y\right)=15\)

\(\Rightarrow x\left(4-y\right)=15=3.5=5.3=1.15=15.1\)  (Vì x,y thuộc N, 15 > 0)

Thay \(4-y=5\Rightarrow y=-1\)

\(4-y=3\Rightarrow y=1\)

\(4-y=15\Rightarrow y=-11\)

\(4-y=1\Rightarrow y=3\)

Vậy \(\left(x;y\right)\in\left\{\left(3;-1\right)\left(5;1\right)\left(1;-11\right)\left(15;3\right)\right\}\)