X+4Y-3Z=0 (1)4X-5Y+2Z=0 (2)(1)*4-(2)16Y-12Z+5Y-2Z=021Y=14ZY:Z=2:3y=2z/3(1)*5+(2)*45X-15Z+16X+8Z=021X=7ZX:Z=1:3x=z/3不妨设z=6a，那么x=2a，y=3a，z=6a（3x²+2xy+z²）/（x²+y²）= （12a²+12a²+36²）/（4a²+9a²）=72/13
6
