Differentiation of sum

Dear Sir:

I have the below sum equation.

Please make some correction to get a solution.

with(student);

v:=(w[j])->sqrt(Sum(A[i]*cos(w[j]*t[i]),i=1..n)^(2)+Sum(A[i]*sin(w[j]*t[i]),i=1..n)^(2));

v(w[j]); diff(v(w[j]), w[j]);

value(%);

 

Thanks