Question
Prove that$$|\mathbf{x}+\mathbf{y}|^{2}+|\mathbf{x}-\mathbf{y}|^{2}=2|\mathbf{x}|^{2}+2|\mathbf{y}|^{2}$$if $\mathbf{x} \in R^{k}$ and $\mathbf{y} \in R^{\star} .$ Interpret this geometrically, as a statement about parallel-ograms.
Step 1
Step 1: Expand the left side of the equation We have: $$|\mathbf{x}+\mathbf{y}|^{2} = (\mathbf{x}+\mathbf{y}) \cdot (\mathbf{x}+\mathbf{y}) = \mathbf{x} \cdot \mathbf{x} + 2\mathbf{x} \cdot \mathbf{y} + \mathbf{y} \cdot Show more…
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Prove that $$ \|\mathbf{u}+\mathbf{v}\|^{2}+\|\mathbf{u}-\mathbf{v}\|^{2}=2\|\mathbf{u}\|^{2}+2\|\mathbf{v}\|^{2} $$ and interpret the result geometrically by translating it into a theorem about parallelograms.
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