Calculus (3rd Edition)

Published by W. H. Freeman
ISBN 10: 1464125260
ISBN 13: 978-1-46412-526-3

Chapter 13 - Vector Geometry - 13.2 Vectors in Three Dimensions - Exercises - Page 660: 54

Answer

The two lines intersect. Intersection point: $\left( {\frac{5}{4},\frac{{11}}{2}} \right)$.

Work Step by Step

The two lines intersect if there exist parameter values $t$ and $s$ such that $\left( { - 1,1} \right) + t\left( {2,4} \right) = \left( {2,1} \right) + s\left( { - 1,6} \right)$ In component forms, we have $ - 1 + 2t = 2 - s$, ${\ \ \ }$ $1 + 4t = 1 + 6s$ Solving the two equations we obtain $t = \frac{9}{8}$ and $s = \frac{3}{4}$. Substituting $t = \frac{9}{8}$ in ${{\bf{r}}_1}\left( t \right) = \left( { - 1,1} \right) + t\left( {2,4} \right)$ gives the intersection point: ${{\bf{r}}_1}\left( {\frac{9}{8}} \right) = \left( {\frac{5}{4},\frac{{11}}{2}} \right)$. Likewise, substituting $s = \frac{3}{4}$ in ${{\bf{r}}_2}\left( s \right) = \left( {2,1} \right) + s\left( { - 1,6} \right)$ also gives the same intersection point: ${{\bf{r}}_2}\left( {\frac{3}{4}} \right) = \left( {\frac{5}{4},\frac{{11}}{2}} \right)$.
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