答：
抛物线y=(1/2)x^2+3x-1与直线y=x-k联立得：
y=(1/2)x^2+3x-1=x-k
(1/2)x^2+2x+k-1=0
x^2+4x+2k-2=0
x^2+4x+4=6-2k
(x+2)^2=6-2k
1）当6-2k>0即k