# Orthogonality from infinitesimal small rotation

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1. May 27, 2015

### Warlord_

Hello buddies,

Could someone please help me to understand where the second and the third equalities came from?
Thanks,

2. May 28, 2015

### DEvens

Um... Ok, it's a little difficult to know what level of detail you want.

The first equation essentially says that the length of a vector does not change under rotations. The second one follows from the first one using the chain rule, and assuming delta of gik is zero.

3. May 31, 2015

### Warlord_

- is vik time dependent? And since it is an infinitely small matrix, the $\delta v^k_i = I$?