Bài 5 :
Ta có : x + y - z = 0
=> x + y = z
x - z = - y
y - z = - x
M = ( 1 + `x/y` )( 1 - `z/x`)( -1 + `y/z` )
M = ( `y/y` + `x/y` )( `x/x` - `z/x`)( `-z/z` + `y/z` )
M = ( `(x+y)/y`)( `(x-z)/x`)( (`(y-z)/z` )
M = `z/y` . `(-y)/x` . `(-x)/z`
M = 1
Vậy M = 1