Precalculus: Mathematics for Calculus, 7th Edition

Published by Brooks Cole
ISBN 10: 1305071751
ISBN 13: 978-1-30507-175-9

Chapter 9 - Review - Test - Page 675: 9

Answer

$\langle \frac{7\sqrt 6}{18}, \frac{\sqrt 6}{9}, -\frac{\sqrt 6}{18} \rangle$ and $\langle -\frac{7\sqrt 6}{18}, -\frac{\sqrt 6}{9}, \frac{\sqrt 6}{18} \rangle$

Work Step by Step

Step 1. Identify the given vectors $\vec u=0i+j+2k$ and $\vec v=i-2j+3k$ Step 2. We know that the cross product of these two vectors will be perpendicular to both, so we have $\vec u\times\vec v=(1\times3-2(-2))i+(2\times1-0\times3)j+(0(-2)-1\times1)k==7i+2j-k$ Step 3. Find the unit vector of the result from step 2: $\vec n=\frac{1}{\sqrt {(7)^2+(2)^2+(-1)^2}}(7i+2j-k) =\frac{\sqrt 6}{18}(7i+2j-k)=\frac{7\sqrt 6}{18}i+\frac{\sqrt 6}{9}j-\frac{\sqrt 6}{18}k =\langle \frac{7\sqrt 6}{18}, \frac{\sqrt 6}{9}, -\frac{\sqrt 6}{18} \rangle$ Step 4. The second normal vector can be the vector opposite to $\vec n$, so that $\vec {-n}=\langle -\frac{7\sqrt 6}{18}, -\frac{\sqrt 6}{9}, \frac{\sqrt 6}{18} \rangle$
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