x大于等于0,y大于等于0,z大于等于0.3x+2y+z=5,2x+y-3z=1,u=3x+y-7z 求u的最值,
问题描述:
x大于等于0,y大于等于0,z大于等于0.3x+2y+z=5,2x+y-3z=1,u=3x+y-7z 求u的最值,
答
y=7-11z
x=7z-3
又x,y,z≥0
得7/11≥z≥3/7
又u=3z-2
得u的最大值是-1/11,最小值是-5/7