# Math Help - find this suffix notation

1. ## find this suffix notation

(i) i got I, (ii) 3I (iii) (3a.(Cb))d - Cd (iv) b X a (v) 0
which one is incorrect???

2. Originally Posted by szpengchao

(i) i got I, (ii) 3I (iii) (3a.(Cb))d - Cd (iv) b X a (v) 0
which one is incorrect???
I'm not so sure about (ii) .....

While it's true that $\delta_{ii} = 3$, and so $\delta_{ii} \delta_{jk} = 3I$, I don't think the summation convention lets you say $\delta_{ii} \delta_{ij} = 3I$ ....