but in this case, we derive with respect to x3 (i=3) which is one term, but the original derivative is with respect to (x_i) which is the whole i's values?!
Thank you PeroK! Even if x_i is an independent variable. why the summation is canceled out? can you explain the derivative in detail, please? and you're right the answer is 2x_i not x_i
Why the summation of the following function will be canceled out when we take the partial derivative with respect to the x_i?
Notice that x_i is the sub of (i), which is the same lower limit of the summation! Can someone, please explain in details?