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: 24

Answer

\[ Q(-4,-3) \text { and } P(4,3) \]

Work Step by Step

(a) The line in two 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: \[ \begin{aligned} \langle x, y\rangle &=\left\langle x_{0}+a t, y_{0}+b t\right\rangle \\ \langle x, y, z\rangle &=\left\langle x_{0}+a t, y_{0}+b t, z_{0}+c t\right\rangle \end{aligned} \] or \[ \begin{aligned} &\left\langle x_{0}, y_{0}\right\rangle+t\langle a, b\rangle=\langle x, y\rangle \\ &\left\langle x_{0}, y_{0}, z_{0}\right\rangle+t\langle a, b, c\rangle=\langle x, y, z\rangle \end{aligned} \] From the parametric equation of the line, we get: \[ \langle 4 t, 3 t\rangle=\langle x, y\rangle \Rightarrow y=3 t \text { and } x=4 t \] If we substituted this into the circuit equation, the result would be: \[ \begin{aligned} 25=y^{2}+x^{2} & \Rightarrow25=(3 t)^{2}+(4 t)^{2} \\ & \Rightarrow 25=9 t^{2}+16 t^{2}\\ & \Rightarrow 1=t^{2} \Rightarrow \pm 1=t_{0} \end{aligned} \] For $\pm 1=t_{0}$, we find that \[ (\pm 4,\pm 3)=\left(4 t_{0}, 3 t_{0}\right)=\left(x_{0}, y_{0}\right) \] So, the line intersects the circle at the points $Q(-4,-3)$, $P(4,3)$
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