Hello. It seems like you're asking about how to take the sum of a series. If you look at the documentation for symsum found at https://www.mathworks.com/help/symbolic/symsum.html, you might find what you're looking for. As a simple example,
syms k x
S1 = symsum(k*x, k, 0, 10)
S2 = symsum(S1,x,0,10)
or more concisely,
syms k x
S = symsum(symsum(k*x, k, 0, 10),x,0,10)
These will take the sum of k * x as x goes from 0 to 10 and take the sum of x * the result of that sum as x goes from 0 to 10. Refer to the linked documentation for more specifics and exmaples on how the symsum function is defined and used.
