3x-y=2k-1 (1)4x+2y=k (2)(1)*2+(2)10x=4k-2+k=5k-2x=(5k-2)/10由(1),y=3x-2k+1=3(5k-2)/10-2k+1x>0,(5k-2)/10>0,5k-2>0,k>2/5y>0,3(5k-2)/10-2k+1>0.3(5k-2)/10>2k-1,15k-6>20k-10,5k0且y>0所以(5k-2)/10>0=>k>2/5
(4-5k)/10>0=>k0,k>0.4再由前式得4x-4/3*y=8/3*k-4/3,y=-0.5k+0.4-0.5k+0.4>0,k<0.8∴0.4<k<0.8 |