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## Homework Statement

I'm having some trouble understanding the Kronecker Delta function and how it is used. I understand the basics of it, if i=j, delta=1, if not, delta=0. However, I don't understand why:

[tex]\delta_{ii}=3[/tex]

and

[tex]\delta_{ij}\delta_{ij}=3[/tex]

## Homework Equations

[tex] \delta_{ij}= \left\{\begin{array}{cc}1,&\mbox{ if }i=j,\\0, & \mbox{ if } i\neq k\end{array}\right.[/tex]

## The Attempt at a Solution

I have not been able to find any proofs using the Kronecker delta online anywhere so I'm not exactly sure of its function. My best guess of why [tex]\delta_{ii}=3[/tex] would be that you take the determinant of the identity function which would give you three. However, I'm not exactly sure what to do for the second one.

Also could someone explain why [tex]\delta_{ii}=\delta_{11}+\delta_{22}+\delta_{33}=1+1+1=3[/tex]? That's what was in my book but they didn't have any explanation of why.