Question

Câu c

Answer 1

Câu c:

\(M=\dfrac{x}{x+y+z}+\dfrac{y}{x+y+t}+\dfrac{z}{y+z+t}+\dfrac{t}{z+t+x}\\ \Rightarrow M>\dfrac{x}{x+y+z+t}+\dfrac{y}{x+y+z+t}+\dfrac{z}{x+y+z+t}+\dfrac{t}{x+y+z+t}=1\)

Mà \(M< \dfrac{x+t}{x+y+z+t}+\dfrac{y+z}{x+y+z+t}+\dfrac{z+x}{x+y+z+t}+\dfrac{y+t}{x+y+z+t}=\dfrac{2\left(x+y+z+t\right)}{x+y+z+t}=2\)

Do đó \(1< M< 2\Rightarrow M\notin N\)