Ta có: `x : y : z = 3 : 4 : 5 => x/3 = y/4 = z/5 = k`
`= >x = 3k ; y = 4k ; z = 5k`
`=> 2x^2 + 2y^2 - 3z^2 = -100`
`=> 2(3k)^2 + 2(4k)^2 - 3(5k)^2 = -100`
`=> 2.3^2 . k^2 + 2.4^2 .k^2 - 3.5^2 .k^2 = -100`
`=> 18 . k^2 + 32 .k^2 - 75 .k^2 = -100`
`=> (18+32-75) . k^2 = -100`
`=> -25 . k^2 = -100`
`=> k^2 = 4`
Xét `k = 2 => x/3 = y/4 = z/5 =2 => x = 6; y = 8; z = 10` (T/M)
Xét `k = 2 => x/3 = y/4 = z/5 =-2 => x = -6; y = -8; z = -10` (T/M)
