If given δ_ijδ_kk what would the expansion of that be? I thought it was nine but have been told that is incorrect. I know that i=j =1 else zero so I thought that the δ_kk would equal 3 times 3 from the expansion of δ_ij but that isn't the answer
Hi cgstu! Welcome to PF!
(try using the X2 tag just above the Reply box )
In δijδkk, which indices are you summing over?