9.已知数列{an}\{a_{n}\}{an}的前8项1,1,2,3,5,10,13,21,令f(x)=∑i=18(x−ai)2f(x)=\sum\limits_{i=1}^{8}(x-{a}_{i})^{2}f(x)=i=1∑8(x−ai)2,则f(x)f(x)f(x)的最小值点x=x=x=[ 7 ].