In one of my hw problems we are asked to prove this:(adsbygoogle = window.adsbygoogle || []).push({});

|X + Y|^2 + |X - Y|^2 = 2|X|^2 + 2|Y|^2

It seems quite simple: I just expanded both of them (cancelled 2(X dot Y) terms) and came up with the expression on the right. Is there something I am missing or is it really that simple?

Thanks !

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# Related to orthogonality

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