|⟨𝒖,𝒗⟩|≤‖𝒖‖‖𝒗‖ Or the more familiar real number version (∑𝑢𝑖𝑣𝑖)2≤(∑𝑢2𝑖)(∑𝑣2𝑖) Related AM-GM Inequality Applications References