Calculus, 10th Edition (Anton)

Published by Wiley
ISBN 10: 0-47064-772-8
ISBN 13: 978-0-47064-772-1

Chapter 11 - Three-Dimensional Space; Vectors - 11.2 Vectors - Exercises Set 11.2 - Page 783: 27

Answer

\[ \vec{w}+\vec{v}=\left\langle\frac{-\sqrt{2}+\sqrt{3}}{2}, \frac{\sqrt{2}+1}{2}\right\rangle \] \[ \vec{v}-\vec{w}=\left\langle\frac{\sqrt{2}+\sqrt{3}}{2}, \frac{-\sqrt{2}+1}{2}\right\rangle \]

Work Step by Step

Let $\vec{v}=\langle a, b\rangle$ be a vector in 2d-space. The base of this vector and angle for the positive $x$ axis are \[ \begin{aligned} &\sqrt{b^{2}+a^{2}}=\|\vec{v}\| \\ &b / a=\tan \phi \end{aligned} \] respectively. So \[ \quad \sin \phi \|\vec{v}\|=b, \cos \phi \|\vec{v}\|=a \] $\vec{v}$ can be written as \[ \vec{v}=\langle a, b\rangle=\langle\cos \phi, \sin \phi\rangle\|\vec{v}\| \] So: \[ \begin{array}{l} \vec{v}=\left\langle\cos 30^{\circ}, \sin 30^{\circ}\right\rangle \|\vec{v}\|=\left\langle\frac{\sqrt{3}}{2}, \frac{1}{2}\right\rangle \\ \vec{w}=\left\langle\cos 135^{\circ}, \sin 135^{\circ}\right\rangle\|\vec{w}\|=\left\langle-\frac{\sqrt{2}}{2}, \frac{\sqrt{2}}{2}\right\rangle \end{array} \] The sum and the difference between these vectors are \[ \begin{array}{l} \vec{w}+\vec{v}=\left\langle-\frac{\sqrt{2}}{2}, \frac{\sqrt{2}}{2}\right\rangle+\left\langle\frac{\sqrt{3}}{2}, \frac{1}{2}\right\rangle=\left\langle\frac{\sqrt{3}-\sqrt{2}}{2}, \frac{1+\sqrt{2}}{2}\right\rangle \\ \vec{v}-\vec{w}=\left\langle\frac{3}{2}, \frac{1}{2}\right\rangle-\left\langle-\frac{\sqrt{2}}{2}, \frac{\sqrt{2}}{2}\right\rangle=\left\langle\frac{\sqrt{2}+\sqrt{3}}{2}, \frac{-\sqrt{2}+1}{2}\right\rangle \end{array} \]
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