Prove that if the vectors a,b parallel, then āxb=0. are %3|

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
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**Proof: If Vectors \(\vec{a}\) and \(\vec{b}\) are Parallel, then \(\vec{a} \times \vec{b} = 0\)**

Vectors are parallel if one is a scalar multiple of the other. This means that \(\vec{a} = k\vec{b}\) for some scalar \(k\).

The cross product of two vectors \(\vec{a}\) and \(\vec{b}\) is defined as:

\[
\vec{a} \times \vec{b} = \|\vec{a}\| \|\vec{b}\| \sin\theta \, \vec{n}
\]

where:
- \(\|\vec{a}\|\) and \(\|\vec{b}\|\) are the magnitudes of vectors \(\vec{a}\) and \(\vec{b}\),
- \(\theta\) is the angle between \(\vec{a}\) and \(\vec{b}\),
- \(\vec{n}\) is the unit vector perpendicular to the plane containing \(\vec{a}\) and \(\vec{b}\).

If \(\vec{a}\) and \(\vec{b}\) are parallel, then \(\theta = 0^\circ\) or \(180^\circ\). Thus, \(\sin\theta = \sin 0^\circ = 0\) or \(\sin 180^\circ = 0\).

Therefore, the cross product becomes:

\[
\vec{a} \times \vec{b} = \|\vec{a}\| \|\vec{b}\| \cdot 0 \cdot \vec{n} = 0
\]

This proves that if vectors \(\vec{a}\) and \(\vec{b}\) are parallel, then the cross product \(\vec{a} \times \vec{b}\) is indeed zero.
Transcribed Image Text:**Proof: If Vectors \(\vec{a}\) and \(\vec{b}\) are Parallel, then \(\vec{a} \times \vec{b} = 0\)** Vectors are parallel if one is a scalar multiple of the other. This means that \(\vec{a} = k\vec{b}\) for some scalar \(k\). The cross product of two vectors \(\vec{a}\) and \(\vec{b}\) is defined as: \[ \vec{a} \times \vec{b} = \|\vec{a}\| \|\vec{b}\| \sin\theta \, \vec{n} \] where: - \(\|\vec{a}\|\) and \(\|\vec{b}\|\) are the magnitudes of vectors \(\vec{a}\) and \(\vec{b}\), - \(\theta\) is the angle between \(\vec{a}\) and \(\vec{b}\), - \(\vec{n}\) is the unit vector perpendicular to the plane containing \(\vec{a}\) and \(\vec{b}\). If \(\vec{a}\) and \(\vec{b}\) are parallel, then \(\theta = 0^\circ\) or \(180^\circ\). Thus, \(\sin\theta = \sin 0^\circ = 0\) or \(\sin 180^\circ = 0\). Therefore, the cross product becomes: \[ \vec{a} \times \vec{b} = \|\vec{a}\| \|\vec{b}\| \cdot 0 \cdot \vec{n} = 0 \] This proves that if vectors \(\vec{a}\) and \(\vec{b}\) are parallel, then the cross product \(\vec{a} \times \vec{b}\) is indeed zero.
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