Answer

• We have $\frac{π}{4}≤ θ ≤ \frac{3π}{4}$:PICTURE polar ineqs 6 with pink Within those values of θ the value of r can be anything nonnegative, the appropriate bound is 0≤ r. It would be possible to describe this region in a way that allowed r to be negative, but there's no need to go to the extra trouble.