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Homework Statement
Show that [tex]\delta_a^b[/tex] is a in fact a mixed tensor of valence (1,1).
Homework Equations
Definition of a (1,1) tensor:
[tex]\delta'_a^b=\frac{\partial x'^b}{\partial x^c}\frac{\partial x^d}{\partial x'^a}\delta_c^d[/tex]
The Attempt at a Solution
So, I just explicitly put back the summations and I get a sum over c from 1 to 4 and a sum over d from 1 to 4 of the above expression. I did the sum over c first and got:
[tex]\sum_{d=1}^4 (\delta_1^d\frac{\partial x'^b}{\partial x^1}\frac{\partial x^d}{\partial x'^a}+...)[/tex]
Where the ... had the [tex]\delta_2^d[/tex] terms etc. I did the summation over d, and I seem to be getting:
[tex]\frac{\partial x'^b}{\partial x^1}\frac{\partial x^1}{\partial x'^a}+\frac{\partial x'^b}{\partial x^2}\frac{\partial x^2}{\partial x'^a}+\frac{\partial x'^b}{\partial x^3}\frac{\partial x^3}{\partial x'^a}+\frac{\partial x'^b}{\partial x^4}\frac{\partial x^4}{\partial x'^a}[/tex]
Which equals:
[tex]4\frac{\partial x'^b}{\partial x'^a}[/tex]
I get the 4 because there's 4 instances where the kronecker deltas don't equal 0 (when d=1 the first term remains, when d=2 the second term remains, etc)...but I really shouldn't have that 4 there. What happened? =(