Chapter 13 - Vector Functions - 13.1 Exercises - Page 870: 14

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Parametric equations: $\left\{\begin{array}{l} x=\cos t\\ y=-\cos t\\ z=\sin t \end{array}\right.$ Because $\sin^{2}A+\cos^{2}A=1$, all the points lie in the plane $y=-x$, and $x^{2}+z^{2}=1,$ so this is a circle in that plane.