设x−12＝2−y3＝z−34=k，则x=2k+1，y=-3k+2，z=4k+3，∵x，y，z均为非负实数，∴2k+1≥0−3k+2≥04k+3≥0，解得-12≤k≤23，于是W=3x+4y+5z=3（2k+1）-4（3k-2）+5（4k+3）=14k+26，∴-12×14+26≤14k+26≤23×14+...