Polarisation Identity
For , .
Lemma 9.8 (Polarisation Identity)
For any ,
Proof
Expanding the squared norm gives
Rearranging yields the polarisation identity.
Related
Stated in
- Lemma 9.8 (Polarisation Identity)§9.3 Orthogonal Groups

Polarisation Identity
For , .
For any ,
Expanding the squared norm gives
Rearranging yields the polarisation identity.