i would have transform each norm into inner product form
and use the distributive law.
That's what they did but in a long, sloppy way:
but here they just do some magic
put out thr Re part
i dont know whats the Re part in that context
, but for some reason I can't understand, instead of cancelling the
two central summands, they thought it'd be a good idea to write
, which seems a pretty goofy and weird thing to do, though the final result still is right.
what method they use here?
as if they say
thats not true its a wrong way of the triangle innequality