1. Let v, w be any two vectors. Prove that ||v + w||² - ||v − w||² = 4v. w W (Hint: Use properties of the dot product. Do NOT use component forms of the vectors.)

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Chapter1: Functions And Models
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1. Let **v, w** be any two vectors. Prove that

\[
\| \mathbf{v} + \mathbf{w} \|^2 - \| \mathbf{v} - \mathbf{w} \|^2 = 4 \mathbf{v} \cdot \mathbf{w}
\]

*(Hint: Use properties of the dot product. Do NOT use component forms of the vectors.)*

2. Suppose that **v, w** are orthogonal. Use Equation (1) to show that

\[
\| \mathbf{v} - \mathbf{w} \| = \| \mathbf{v} + \mathbf{w} \|
\]

3. Let **x, y** be any two vectors. Assume that

\[
\| \mathbf{x} + \mathbf{y} \| = \| \mathbf{x} \| = \| \mathbf{y} \|
\]

Find the angle between **x, y**.

*(Hint: Begin by squaring both sides of the first equation given above. Alternatively, use geometry as a guide. Your proof cannot rely on geometry, but it is a strong starting point.)*

4. Use the 3-space standard basis vectors to find three nonzero vectors **a, b, c** satisfying **a × b = a × c**, where **a × b ≠ 0** and **b ≠ c**.

*(This proves that the cross product operation does not have cancellation across equations.)*
Transcribed Image Text:1. Let **v, w** be any two vectors. Prove that \[ \| \mathbf{v} + \mathbf{w} \|^2 - \| \mathbf{v} - \mathbf{w} \|^2 = 4 \mathbf{v} \cdot \mathbf{w} \] *(Hint: Use properties of the dot product. Do NOT use component forms of the vectors.)* 2. Suppose that **v, w** are orthogonal. Use Equation (1) to show that \[ \| \mathbf{v} - \mathbf{w} \| = \| \mathbf{v} + \mathbf{w} \| \] 3. Let **x, y** be any two vectors. Assume that \[ \| \mathbf{x} + \mathbf{y} \| = \| \mathbf{x} \| = \| \mathbf{y} \| \] Find the angle between **x, y**. *(Hint: Begin by squaring both sides of the first equation given above. Alternatively, use geometry as a guide. Your proof cannot rely on geometry, but it is a strong starting point.)* 4. Use the 3-space standard basis vectors to find three nonzero vectors **a, b, c** satisfying **a × b = a × c**, where **a × b ≠ 0** and **b ≠ c**. *(This proves that the cross product operation does not have cancellation across equations.)*
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v+w2-v-w2=4v·w

 

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