MATLAB: Why this code involving symsum doesn’t work

symsum

I am supposed to create a function that can compute the formula in the attachment. But the the variables x and n in my_sin(x,n) don't sync with the one in symsum.
it will be very helpful if someone can tell me where is wrong.
function y = my_sin(x,n)
syms x n 
outputArg1 = x;
outputArg2 = n;
y=symsum([-1^n]*[[x^2*n]+1]*[1/factorial(2*n+1)],n,0,n);
end

Best Answer

Variable of summation is 'i'. Try this code
function y = my_sin(x,n)
    syms I
    y=symsum((-1^I)*x^(2*I+1)/factorial(2*I+1),I,0,n);
end
Run it like this
>> my_sin(1, 2)
ans =
-47/40
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