(1)∵x1,x2是方程x^2-6x+k=0的两个根,∴x1+x2=6,x1x2=k,∵x1^2×x2^2-x1-x2=115,∴k^2-6=115,解得k1=11,k2=-11,当k1=11时,△=36-4k=36-44<0,∴k1=11不合题意当k2=-11时,△=36-4k=36+44>0,∴k2=-11符合题意,∴k的值为-11;(2)∵x1+x2=6,x1x2=-11∴x1^2+x2^2+8=(x1+x2)^2-2(x1x2)+8=36+2×11+8=66.