1. The problem statement, all variables and given/known data Given a tensor Mab, Prove that its trace is a scalar. 2. Relevant equations 3. The attempt at a solution To prove the trace is a scalar, I know I have to prove it doesn't transform under coordinate transformations. Now, we can transform M^a_b as follows. M'cd=(dx'c/dxa)(dxb/dx'd)Mab For the trace Maa, the transformation is as follows. I've used the Kronecker delta for changing Mab to Maa. ( Am I along the right lines in doing so?). M'cd=(dx'c/dxa)(dxb/dx'd)Mab(Kronecker deltaab) Then I thought using the delta I change dxb to dxa and cancel the two dxa. However that would then the delta away from Mab, leaving it as Mab as before rather than Maa. That's the best I can do, please help.