a, \(x-y=2\left(x+y\right)\Rightarrow x-y=2x+2y\Rightarrow x-2x=y+2y\Rightarrow-x=3y\Rightarrow x=-3y\)\(\left(1\right)\)
Thay (1)vào x - y = x : y \(\Rightarrow-3y-y=-3y:y\Rightarrow-4y=-3\Rightarrow y=\dfrac{3}{4}\)\(\Rightarrow x=\dfrac{3}{4}.\left(-3\right)=\dfrac{-9}{4}\)Vậy \(x=\dfrac{-9}{4};y=\dfrac{3}{4}\)
b,\(x+y=x.y\Rightarrow x=x.y-y\Rightarrow x=y.\left(x-1\right)\left(2\right)\)
Thay \(\left(2\right)vào\)\(x+y=x:y\Rightarrow x+y=\dfrac{y.\left(x-1\right)}{y}\Rightarrow x+y=x-1\Rightarrow y=-1\left(3\right)\)
Thay \(\left(3\right)\)vào x + y = x . y\(\Rightarrow x-1=x.\left(-1\right)\Rightarrow x-1=-x\Rightarrow x+x=1\Rightarrow2x=1\Rightarrow x=\dfrac{1}{2}\)
Vậy y = -1 và x = 1/2
