(1) ka+b=(k-2,5k+3,-k+5 )
a-3b=(7,-4,-16)
7=m(k-2)
-4=m(5k+3)
-16=m(-k+5)
解得 k=-1/3
(2)垂直,则点积为0
7(k-2)-4(5k+3)-16(-k+5)=0
3k=106
k=106/3