Đáp án:
`a) .... = (x+y)/(5-3) = 34/2 = 17`
` => x = 85`
` => y = -51`
`b)`
` ..... = (x-5+y-4 + z-3)/(3+4+5) = ((x+y+z) -12)/12 = 2`
` => x -5 = 6 => x= 11`
` y-4 = 8 => y = 12`
` z-3 = 10 => z =13`
`c)`
Đặt ` x/5 = y/4 = z/2 = k`
` => x = 5k ; y = 4k ; z = 2k`
` x^3 - y^3 +z^3 = 69= 125k^3 - 64k^3 + 8k^3 = 69`
` => 69k^3 = 69`
` => k = 1`
` => x = 5 ; y =4 ; z = 2`