答：x1^2+x2^2=6(x1+x2)^2-2x1*x2=6(k+1)^2-2(k+2)=6k^2-9=0k=3或者k=-3因为Δ=（k+1)^2-4(k+2)>=0即：k^2-2k-7>=0k>=1+2√2或者k=<1-2√2故k=3不符合需舍去。综上所述k=-3
