why this code involving symsum doesn't work

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

[Qiao Wei Ting]

my_sin(1, 2)

ans =

- (8178130767479*x^2)/44460928512000 - 603180793741/513257472000

the answer appears to be like this.

Answer 1

[Ameer Hamza]

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

[Qiao Wei Ting]

Got it! thanks a lot