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Re(<x,(<x,e_1>+........<x,e_k>)e_n>)= |<x,e_1>|^2+........+|<x,e_n>|^2

I got <x,(<x,e_1>+........<x,e_k>)e_n>= <<x,e_1>e_1,x>+......<<x,e_n>e_n,x>

but haven't a clue how to find the real part of this. Sorry for the ugly subscript notation.