因为,|(1/2)x-2y| ≥ 0 ,|y-1/2| ≥ 0 ,且已知,|(1/2)x-2y|+|y-1/2| = 0 ,所以,|(1/2)x-2y| = 0 ,|y-1/2| = 0 ,可得：(1/2)x-2y = 0 ,y-1/2 = 0 ,解得：x = 2 ,y = 1/2 ,可得：7x-3y = 12.5 .