x1+x2=k-1
x1x2=-3k-2
x1²+x2²=(x1+x2)²-2x1x2=17
k²-2k+1+6k+4=17
k²+4k-12=0
(k-2)(k+6)=0
k=2,k=-6
且△>=0
(k-1)²+4(3k+2)>=0
k=-6不成立
所以k=2