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I try to make a summation list and the commands are below this:

sage: var('n')

sage: var('x')

sage: f = (2/n)(sin(nx)*(-1)^(n+1))

sage: funclist = [sum(f,n,1,20) for n in range(1,3)]

but i found an error message:

TypeError: need a summation variable

How to solve this problem?

I try to make a summation list and the commands are below this:

sage: var('n')

sage: var('x')

sage: f = (2/n)(sin(nx)*(-1)^(n+1))

sage: funclist = [sum(f,n,1,20) for n in range(1,3)]

but i found an error message:

TypeError: need a summation variable

How to solve this problem?

I try to make a summation list and the commands are below this:

sage: var('n')

sage: var('x')

sage: f = (2/n)(sin(nx)*(-1)^(n+1))(2/n)*(sin(n*x)*(-1)^(n+1))

sage: funclist = [sum(f,n,1,20) for n in range(1,3)]

but i found an error message:

TypeError: need a summation variable

How to solve this problem?