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 - 11.5 Parametric Equations Of Lines - Exercises Set 11.5 - Page 811: 28

Answer

The line intersects the plane at $P(5 / 4,9 / 4,1 / 2)$

Work Step by Step

(a) The line in 2d space that passes through the point $P_{0}\left(x_{0}, y_{0}\right)$ and that is parallel to the non-zero vector $\mathbf{v}=\langle a, b\rangle=a \mathbf{i}+b \mathbf{j}$ has parametric equations \[ b t+y_{0}=y, \quad a t+x_{0}=x \] (b) The line in 3d space that passes through the point $P_{0}\left(x_{0}, y_{0}, z_{0}\right)$ and that is parallel to the non-zero vector $\mathbf{v}=\langle a, b, c\rangle=a \mathbf{i}+b \mathbf{j}+c \mathbf{k}$ has parametric equations \[ c t+z_{0}=z, \quad b t+y_{0}=y, \quad at+x_{0}=x \] The vector equations of these lines can be written as: \[ \begin{aligned} &\left\langle x_{0}+a t, y_{0}+b t, z_{0}+c t\right\rangle =\langle x, y, z\rangle \\ &\left\langle x_{0}+a t, y_{0}+b t\right\rangle =\langle x, y\rangle \end{aligned} \] or \[ \begin{aligned} &\left\langle x_{0}, y_{0}, z_{0}\right\rangle+t\langle a, b, c\rangle=\langle x, y, z\rangle \\ &\left\langle x_{0}, y_{0}\right\rangle+t\langle a, b\rangle =\langle x, y\rangle \end{aligned} \] It's given the parametric equation of the line is: \[ 2 t-1=z, \quad 3 t=y \quad, \quad 2-t+2=x \] Replace this in the equation of the plane to get: \[ \begin{aligned} 6=3 z+2 y & \Rightarrow 6=(2 t-1)3+(3 t)2 \\ & \Rightarrow 6= 6 t+6 t-3\\ & \Rightarrow 9=12 t \\ & \Rightarrow 3 / 4=9 / 12=t \end{aligned} \] For this value of $f$, we get: \[ \begin{array}{l} z=-1+2 t=-1+\frac{3}{2}=\frac{1}{2} \\ y=3 t=3(3 / 4)=9 / 4 \\ x=2-t=2-3 / 4=5 / 4 \end{array} \] This means that the line intersects the plane at $P(5 / 4,9 / 4,1 / 2)$
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