What language are you using here? Possibly not MATLAB. :)
Do you think that squares the number i, and then multiplies the square of that value by the vector L? After all, * tells MATLAB to multiply two things.
Or, did you want to access the i'th element of L, and then square it? But L is itself only the length of the vector x, so just the number of elements in x.
Or, do you relly want to access the i'th element of the vector x, square THAT, and then sum the result into s?
The code you wrote will not achieve the latter. For that to happen, you would need to write this: