Chapter 10 - Parametric Equations and Polar Coordinates - 10.3 Exercises - Page 687: 9

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Since $r\geq 0$, the terminal sides of all points of the region will be between $\displaystyle \frac{\pi}{4}$ and $\displaystyle \frac{3\pi}{4}$. The border rays are included (the $\leq$ sign includes equality).