In[]:=
f[α_]:=-2*Sum
x1
x[i]
^α*Log
x1
x[i]

1+
x1
x[i]
^α
,{i,2,k}+SumLog
x1
x[i]
,{i,2,k}+
k
α
In[]:=
D[f[α],α]
Out[]=
-
k
2
α
-2
k
∑
i=2
2
Log
x1
x[i]

α
x1
x[i]
1+
α
x1
x[i]
-
2
Log
x1
x[i]

2α
x1
x[i]
2
1+
α
x1
x[i]