Derivatives,

How do I find the derivative of a sumation ? (eg. https://www.dropbox.com/s/3un7mqdg9pjloxm/Screenshot%202016-02-02%2017.34.50.png?dl=0)

Question

Derivatives,

How do I find the derivative of a sumation ? (eg. https://www.dropbox.com/s/3un7mqdg9pjloxm/Screenshot%202016-02-02%2017.34.50.png?dl=0)

hartnn · Answer

term by term.

derivative of (x1 - u)^2 will be -2(x1-u)
right?

same for all terms.

hartnn · Answer

so,
$\Large -2 \sum \limits_{i=1}^{n}(x_i-\mu )$

try 2nd derivative also :)

hartnn · Answer

http://www.sosmath.com/diffeq/series/series02/series02.html

welshfella · Answer

I might be missing somethin - but why -2

christos · Answer

why did it become negative @hartnn

welshfella · Answer

- we though alike!

zarkon · Answer

chain rule

zarkon · Answer

$$\frac{d}{d\mu}(x_i-\mu)=-1$$

welshfella · Answer

oh yes - the variable is the greek letter mu  not the x.

hartnn · Answer

chain rule, 
$\mu $ is the variable, $x_i$'s are constant.

same as finding derivative of (a-x)^2.